Well you should!!!!
There are lots of reasons to have a practise swing before each shot
1. It slows you down,
2. Gets you focusing on the shot
3. Acts as a rehearsal for the shot you are about to play.
Sometimes the ball is above or below your feet or in a heavy lie or you might be playing a shot with less than a full swing,
all good reasons to have a practise swing.
(I know you are thinking it will make you too slow, but you are entitled to one practise swing and once you get into the routine of it, it will not take you very long)
Oh, and I mean EVERY time, chipping, pitching and even putting included, its great for putts as a rehearsal for the length of backswing and through swing you need.