Yup. If we're going to use math to justify this, basically for a 50" TV, 1080p is fine after
~6 feet away from the screen.
http://s3.carltonbale.com/resolution_chart.html
If you go significantly bigger than 50" at a 6' seating distance, then there is potential benefit for 4K, but most people would find that a bit uncomfortable. People buy bigger TVs when they sit further away. Most don't generally buy 70" TVs to sit 6 feet away from it. Plus, those numbers are calculated using the assumption the viewer has perfect vision.
There is more benefit for TVs beyond 70" and projector images, and according to that graph I should be using 4K for my 10 foot seating distance from a 90" image, but right now I'm rockin' just a 720p projector and have no real complaints, although part of that reason is because the projector uses Smooth Screen which is basically a slight sort of defocusing to blur the pixels to minimize screen door effect. Does that affect clarity and text? You bet.... but for movie viewing it's actually nice, and I'm not reading a computer screen, I'm watching a movie. Yeah, I'll upgrade eventually to 1080p, but that's where I'll stop.
However, I own a home theatre projector. I am part of the TV viewing 0.01%. For mainstream TV use, 1080p is more than sufficient and there's no real point in going beyond that, for over 99% of the population.