Plenty of guitar players seem to use closed-eyes, but for all I know that's just so they look cool to the audience.
I don't think it's just to look cool. Our perception of the world completely changes with eyes closed. As our brains have less information to process we get more responsive to other senses. It's not unusual that people who lose their sight have other senses sharpened, like hearing, touch or smell and taste.Notice that, when listening music with eyes closed (especially in the darkness) you can turn the volume down and still hear more details than with eyes open.I myself also close my eyes when I want to hear my music and not just play it, but not for long because it usually ends with disaster
This may not be what you're looking for, but supposedly the Chicago blues pianist Otis Spann favored turning out the lights in the studio, at least sometimes, leading to performances like "Otis in the Dark."I think Garth Hudson from The Band did quite a bit of eyes-closed playing, but that's just a guess.Of course there are any number of blind (or nearly so) pianists, but that's not really a performance choice.I do find it more common, at least in various kinds of group improvisation settings, keeping eye contact with the drummer or the bassist, or even maintaining eyes on the audience, say, sort of counts as not looking at the keyboard, but that's not quite the same thing.Plenty of guitar players seem to use closed-eyes, but for all I know that's just so they look cool to the audience.
Playing without looking is imperative if you are singing into a mic while playing. One cannot move the lips away from the mic to look at keys or frets.