PGA of America Professional Bradley Clayton says that you should release your back foot for crisp pitch shots.
The most common flaw I see in pitching is swinging flat-footed. By this I mean the trailing foot. Releasing the trailing foot (letting it roll towards the toe) makes it easier for the player to keep the hands in front of the club head. This makes crisp contact with the ball much easier as the club head approaches the ball with descent, striking down and through the ball.
When the trailing foot remains flat on the ground, the head of the club will tend to pass the hands and approach the ball at an angle too shallow to make consistent crisp contact. The shots that result may be fat one time or thin the next. So, release your trailing foot, keep those hands in front, and watch your pitching improve.
A good drill for practicing is to take your set up and then roll your trailing foot towards the toe. This will shift your weight more to the forward foot and put you close to your finish position. It will also encourage the lower body to remain quiet in the backswing. Hit some pitch shots from this position and feel how much easier it is to lead with the hands through the shot, creating crisp, consistent shots.