Pitching is like real estate, LOCATION LOCATION LOCATION. Unless you are throwing 12-15mph above the average for your age group, flat and fast will get hammered! Give me a pitcher with average to below average speed that can hit a spot and make a pitch move any day. Back to the original post, you should never slow down a pitch to gain control of the pitch. having said that, I have seen girls that throw so fast they lose control of their body and that needs to be slowed down, but at that point we are talking about poor mechanics. If you slow your pitch down to try to "aim" where it goes, you will lose every time, and as you progress you will have to start to throw harder to keep up with your peers and all of the control you "gained" from slowing down is out the window. As so many have stated here, master the mechanics of the basic fastball, and then add the junk.