As an Editor I can tell you what happens in the end - I get footage from several DPs & Production companies. I mainly do content for large companies Samsung, Intel, etc - they are paying top dollar to put something out. Whats my point ? For Top Dollar they want 2k / 4 K footage . However in Post I've never ever crafted/exported anything above 1920x1080. if you are shooting something to be projected say a short of feature film - shoot 4k 24fps. If its commercial or personal content taht will most likely be a you tube or vimeo share. 2k 24fps is fine. Having said that

4k is nice when we want to re frame the shot - Imagine as a photographer fine tuning a still in photoshop - 4k allows us to do that with video.