2 8K TVs, 6 Months of Use, 6 Takeaways
Working daily with four modern TVs at the same time leads to some useful findings

As May 2021 is now upon us and tech journalists are receiving the first wave of 8K televisions of the year for review, yours truly also noticed a personal milestone of sorts: it's also been 6 months since he's been working with two 8K televisions day in and day out. First it was the LG 75NANO99 (the review of which can be found in this Medium story), then it was the Sony 85ZH8 (that review can be found in this Medium story). Both 8K TVs are very good, the Sony actually recognized by multiple outlets as the best 8K LCD TV of 2020 in picture quality terms.
In the same workspace, there's a Sony 85XH90 (full review in this Medium story), plus one of the best TVs ever built by Sony, the now outdated but still remarkable (because of its amazing local dimming) 75ZD9. I've been watching many, many movies and TV shows, following a few tennis tournaments and playing a number of recent games with a PS4, a PS5 and a gaming PC during these last six months on all four TVs - sometimes on different occasions, other times with the same or similar content.
So! What did I actually learn about 4K and 8K, in practical terms, by using all four models day-in, day-out? Quite a few things, as it turns out, but I handpicked some of those because they may be of interest to people looking for getting a new 4K or 8K TV in 2021.
8K TVs are not worth buying in less than 75 inches
It’s a topic already discussed ad nauseam but, in practice, there's little room for debate: in typical viewing distance (2.5-3.5m in most cases) most people will not be able to discern the level of visual information an 8K TV offers unless it's a 75-incher or larger. On smaller screens the picture will look denser, yes, but most of the details that make quality content so enjoyable in 8K will not be appreciated by the majority of consumers. A few manufacturers do promote 8K TVs at 65 inches and there are a handful of reasons why those may be preferable to equivalent 4K models - they e.g. often sport a better backlighting system, which does make a difference - but those reasons do not have to do with resolution. An 8K TV at 65 inches can be used as an excellent PC monitor... maybe. But for 4K upscaled or 8K native (at some point) content, a screen diagonal of 75 inches is practically a must - for people who don’t like throwing away money, that is.

8K TVs are totally worth buying for movies on UltraHD Blu-ray discs
Since 8K content is practically non-existent right now, most 8K TVs getting into people's homes will have to work with lower resolution content for the foreseeable future. The higher quality of that content is to begin with, the better results one can expect 8K TVs to deliver - and, for movies and documentaries at least, there's no match for a good UltraHD Blu-ray transfer. Watching top-quality UHD BD discs like Dunkirk, Soul, Wonder Woman 1984 or John Wick 3 - or maybe documentaries such as Planet Earth II, Dynasties or Blue Planet II - on an 8K TV is an amazing experience. The upscaled picture is not as breathtakingly spectacular as true 8K content, but it's close. Because of the extra pixels it also looks much more solid and lifelike than on a 4K TV of the same diagonal. Μost UHD BD movies were not mastered in full 4K resolution, yes, but it's the best visual quality available on the market and people collecting those discs will not regret upgrading to a good 8K TV (75 inches or more).
8K TVs are not worth buying for over-the-air programming or DVD discs
For the exact same reason why an 8K TV is worth it for watching movies or documentaries on UltraHD Blu-ray, it's just not worth it for content that is of low quality to begin with, such as over-the-air TV programming or movies on DVD. These TVs do feature powerful image processing chips that help a lot with the upscaling of 1080i- or 576p-resolution content to 4320p but... let's be honest here: all they can accomplish for sub-2K picture is to not look terrible when blown up in 75 or 85 inches. An 8K TV has to literally "create on the fly" more than 30 of the 33 million pixels making up the picture they display when fed content of such low resolution. It's almost miraculous that they manage to do so in real-time. So... no: for people planning to watch just DVDs and the evening news on their new TV, the purchase of a top-of-the-line 8K TV is not exactly money well-spent.

8K TVs are worth buying for streaming... as long as it's 4K streaming
Rounding off the whole "what content is an 8K TV worth buying for" thing one has to include Internet streaming - and after hours and hours (and hours) of watching Netflix, Apple TV Plus, Disney Plus and YouTube movies, shows and videos, this I can confirm: it... depends. It sounds like a cop-out but it's not. It has to do, again, with the quality this content is offered at originally. Some Apple TV Plus 4K content, for instance, looks amazing because this is the streaming service with the highest average video bitrate at the moment. Some Netflix 4K content (mainly Originals) does look spectacular too, despite the fact that it's offered at half the bitrate of the aforementioned Apple TV Plus content. Disney Plus's material varies on resolution and bitrate but it falls somewhere between Apple TV Plus and Netflix most of the time. YouTube is unsurprisingly the least impressive source of the four, video looking decidedly soft even when the video in question is of 4K resolution (Google's compression is quite aggressive). It still beats hands-down DVDs or over-the-air programming, though, so for people planning to do a lot of streaming, an 8K TV will serve them well.
8K TVs are not ideal for gaming (yet)
This comes as no surprise to people actually into games, but for anyone else, it's worth highlighting: video games are not ready for 8K and most people should not buy an 8K TV for gaming. If they buy it for general use and plan to play some games on it, while accepting a number of compromises in the process, great. But "8K gaming" is not a thing yet. On the PC side, the only graphics card capable of even attempting to render modern games in 8K resolution is the super-expensive nVidia RTX 3090 (good luck finding one of course) and even that uses AI-based upscaling (DLSS) in order to approach true 8K. The PS5 or Xbox Series X will probably get 8K output but it's now clear that they are not as powerful as they'd have to be in order to display 8K AAA games. Then it’s the 8K TV models themselves: the vast majority of those do not support the all-important VRR function at 8K and those that do (mainly OLED ones) are prohibitively expensive. Playing at 4K/120 is not an 8K-only feature. So, all in all, just people who want to play 4K/60 games on a really big screen (75''-85'') will benefit from the more dense, detailed picture of an 8K TV. But that is not really "8K gaming", is it?

8K TVs are not worth the price difference for most people - for now
This last point may sound controversial - and it will surely seem so to demanding consumers asking for the best possible image quality on a new TV - but, as far as the great majority of consumers out there is concerned, it's true. Upscaled, quality 4K content on a big 8K TV is all well and good, extremely good even, but the amount of money spent for the privilege is disproportionate. Right now, and for all of 2021 as it would seem, consumers are paying a hefty premium for the increase in resolution that makes the picture of movies or shows seem more convincing and detailed. One only has to watch some actual 8K content on an 8K TV (only possible with a PC equipped with a modern graphics card for now) to understand that. The only reason discerning consumers would be better served by an 8K TV is the advanced display tech that manufacturers reserve for those models instead of the 4K models. There will always be people who demand and can afford what's currently the best tech available but, for the rest of us, a quality 4K TV would probably be a wiser choice. For now.