To begin with, I shoot at 30 fps, not 24, because it's smoother and my footage isn't going to be projected in a movie theater. Then I shoot in 4k simply because it gives me more resolution to work with in editing, so I can crop the image, straighten it or zoom in on it without losing much, especially if I render in 1080p.
That said, I tend to render in 4k, because I do have a 4k TV.