It depends, if you are going to accompany people or sight-read alot, you should lean towards not looking at the keys since there are so many other things you have to pay attention to: sheet music, soloist, ensemble, conductor (if there is one). If you're heading towards just playing solely, you should plan on memorizing your pieces and then you can look at your hands without sheet music distracting you. However, I've found sometimes when I trully have a piece memorized, I'll look away from the keys or close my eyes, and I feel more expressive than I normally do when just looking at the keys.