You are not compromising the snap at all; in fact, if done properly, you are actually ingraining it in your 'large muscle memory'. When practicing in this fashion, at a snail's pace, you start from the ground and work up, just like when you punch for real. Using the straight right as an example, you begin by shifting the body weight over a straight left leg-slowly and emphatically you do this- and then the hips are turned through the center-line then the shoulders. All this at half speed. Then with a sudden and violent twist of the hips and shoulders that begins with a pivot inward on the right toe, drive your right arm into complete extention. If you have ever seen Arguello fight it was almost as if he were using that method- no hand speed, no muscle until the last instant.