The dynamic start is more of whatever is comfortable for the lifter. Not all are the same. It's used to set the torso in a good strong position to lift the bar off the floor.
Usually the hips are moving into the starting position, then the lifter lifts the bar from the floor without the hips stopping. If you look closely at a side angle of lifters that have a comfortable dynamic start, their hips will get very low and this tends to bring the shoulder behind the bar. If you remember in Greg's book it says you want the shoulders just slightly in front of the bar. The lifter has to move into the correct position before the bar leaves the ground so the lifter does not lift the weight while they're moving into the starting position.
For a beginner (possibly intermediate lifter as well), I would recommend a static start so that you can train the body to learn that correct starting position. That way, if you ever wanted to change to a dynamic start, you're body naturally will start to lift the bar when you're in the correct position without throwing anything off.
Let me know if you have anymore questions.