I also have noticed/used this. If I am ahead in a count and feel a high/inside fastball is the pitch I need to throw, I will purposely overthrow it to get more velocity and rise on it. I do not keep charts, but personally I do feel like it changes the way the location of the pitch.
Honestly, without inside knowledge as to how the pitching actually works we may not ever know. I feel like somewhere I read a tip claiming that tapping a pitch gives best chance for high accuracy and holding increases velocity, but lessens control. It makes sense that when you throw a pitch there is some randomness involved (I think we can all agree on that). Tapping would then lessen the weight of this randomness and holding it down would increase it. I would also assume that all pitches have a sort of "bad/unwanted movement" associated with them, for example a slider over-breaking or a fastball rising (which is what in a bad situation you do not want these pitches to do).
I hope more people look into this and maybe we can more clearly understand exactly what is going on, if anything at all.