You can play movie files in Windows on larger screens. Smaller files are nice too.
True but those are software based players and usually zoom in a little to fill the screen completely. TV screens don't work like that. Unless the movie is shot in 16:9 or 16:10 adaptive widescreen there will be black bars. If your cropped image doesn't use the full TV screen, then the TV will simply add the bars back to obtain optimal screen use.
Great, e.g. Kodi automatically displays this correctly on a 21:9 screen.A Cinemascope zoom/crop feature will definitely be added once the really heavy stuff is done.
Note, though, that removing the black bars will not result in smaller files. AVC compresses these black areas down to practically 0 bytes.