Total muscle control requires superb balance, tendon strength, dense muscles and perceptual awareness of everything that goes into maintaining a fighting stance. Slow execution moves challenge all your muscles and they are a favorite of Shaolin Kung Fu specialists and Tai Chi practitioners alike. The trick here is not to just execute each move but to do so by flexing the muscles involved at the end of each one so that they work, as you hold the move in position, like they would had you executed it fast.
The technique is a favourite one of boxers who execute slow punches this way. It makes them faster and stronger without adding on bulk that requires more energy to carry around during a fight.