Poor aim or just need a refresher on how it is done.
Standing up as you swing because your sense of balance tries to keep you from falling down the slope or swinging too flat and hitting the ground before you make contact with the ball.
Doglegs forcing you to play safety shots.
Need to avoid obstacles in the fairway or make it around a dogleg with a powerful shot.
Addressing the ball with your shoulders aligned too far to the left will cause you to slice. Many people make the mistake of lifting their left heel during the backswing, which is one of the most common causes of a slice.
You need a fade without hooking or drawing the ball.
Needing a draw or a fade to make it around doglegs or other obstacles.
Trouble finding the correct distance between you and the golf ball.