... when you have to carry a bunker or don't have much green to work with.
High shots eliminate any trouble between you and your target.
On your backswing, cup your left wrist (bend it back), which will open the clubface and add loft to the shot.
You'll know you're doing it right if you look down and can see the logo on the back of your glove.
...when the front of the green is open or you have a lot of green to work with.
Hitting it low and letting the ball run means you don't have to hit the ball a perfect distance in the air.
Bend your left wrist forward on your takeaway. This bowing action closes the clubface and takes loft off the club.
If you look down at your hands and can't see the logo on your glove, you're doing this right.