What is/are the use case(s) for these things?
Still not sure. I have two old, working laptops now, still don't use one as a NAS or a spare desktop etc.
I have a ordinary laptop, I run a 10m HDMI cable to my TV.
It works without problems and would be ok for almost any sized room. I don't have Netflix on the TV so I run it on the laptop, the UI is simpler to use anyway since the TV doesn't have a keyboard (although it can).
The TV has freeview so I don't need a separate tuner, many TVs have this feature I believe. This TV also allows a normal USB hard drive (or stick) for DVR use. I plugged a standard 1TB WD drive that was super cheap to do DVR work, the only downside is the poor Samsung interface.
I occasionally use iPlayer et al, they work better on the laptop also. Having the TV as a second screen is good for looking at youtube videos together.
I am also able to use my laptop as a computer, surf the web and edit documents, write mail etc., all at the same time.
The laptop can be kept on for very little money, I can access it remotely from my phone if absolutely required (it rarely is anymore).
If torrent downloads were not super fast now and TV not that important, I could remotely control my uTorrent client.
I can have massive storage wirelessly or attached to the laptop but there is little need to keep a large library of video ready all the time.
I get that some people do want different things but is there a need to have a computer you have to remotely access in order to do things like download something or run Netflix?
So, as a nice small desktop a la mac mini for those with limited space who don't want a laptop for some reason, yes. But I fail to see the NAS thing, never have.