Of the 4 basses I currently own that I would say are "in commission and ready to go", 3 have flats on and 1 has rounds on.
I'm not a huge fan of rounds, nor of using a pick, but I do play it, and sometimes with a pick.
Why bother?
Well, sometimes the music requires it, sometimes I fancy the change, and sometimes I just want to, or can do. So I do.