The fact of the matter is the higher the velocity and the better the "stuff", then in general the larger margin of error for the pitcher. This can mean several things. For one, the pitcher can generally get away with worse control/command because the better stuff can hide some of those flaws.
It also often means that a pitcher will get more opportunities to fail. This is true because teams and scouts can dream about what the pitcher could become if he ever puts it all together. Look at Daniel Cabrera, former Oriole pitcher. As an O's fan, I suffered through about five years of his act, always thinking this could be the year or the start that he turns it around. He even started off really well one season (2007 maybe), but it became clearer and clearer that he wasn't going to cut it.
But the point is he got five years worth of MLB opportunities (plus his minor league experience/opportunities) because he could threw easy cheese (97+ with little effort) with a devastating slider.