I can't wait to read all the responses to this one. My opinion comes from a developmental standpoint (getting players to the big leagues).
The worst thing you can do for a young pitcher is tell him to "just throw strikes". What is easier to do...Get a pitcher with a 95 mph fastball and suspect command to throw a strike or get an 82 mph strike thrower to throw the ball 95 mph? It's a ridiculous question but it illustrates the correct developmental sequence. Learn to throw hard first, then learn command. By easing up to "just throw strikes" the body becomes conditioned to operate in that manner and loses a lot of it's explosive capabilities.
Part of throwing the ball hard is trying to throw it hard. This means incorporating momentum into the delivery and really letting the ball go. Let the coaches in the minor leagues tell you when to take a little bit off.
If you are a high school pitcher who throws 80 mph and gets everybody out, you will not get drafted. If you don't get anybody out and throw every 3rd pitch off the backstop at 95 mph you are a pro prospect. It's that simple.
The same goes for hitting. Parents clap when little leaguers hit the ball. No!!! Clap when they hit it hard. Baseball guys have a name for hitters who swing to just hit the ball...They call them outs!