Export at 1080p or 4K?

Hi, i tried to export an edited video on 1080p as a default, and then at 4k (same by phone or pc, there i have to put the right pixel number), but didn't noticed real change, apart of course the size of the file...same with bitrate, i putted 50 instead of 25 and apart the doublesize of the file, didn't noticed something changed...is it useful?