Slow fire serves several purposes. It builds visual skills in the form of a classical "target shooting" type of focus. It works the muscles as far as maintaining a refined wobble zone, and it is useful for developing superior fire control.
For the average undisciplined shooter, dumping mags into the berm as fast as you can pull the trigger perhaps serves no useful purpose, and indeed erodes the fundamentals of shooting. For someone who knows what they are doing, dumping a mag into a target, or into the berm for that matter, builds high speed visual skills, develops neutrality in the grip, is great for overcoming trigger freeze, and enables a shooter to determine the timing of the gun/ammo combination.
The fact is, most shooters will never be good at shooting with a great deal of precision with a handgun. I am talking Master or better in a discipline like Bullseye. Even fewer shooters will really understand what it's like to drive the gun fast and somewhat accurately while "in the zone" like some Master and most Grand Master IPSC shooters do on a regular basis.
For accomplished shooters, there is plenty of room for precision shooting and for hosing.
