I think Maestro Berman said it well, yet from my own experience, over-practicing is less a problem than failing to listen attentively through every phase of learning a composition. If a student does not fine tune each repetition, but considers only right notes in fast speed as the desired end, then phrasing, nuance and aesthetics, are unfortunately lost in the shuffle.
I use an example from my own practice room: a tricky 64th note passage in the Adagio movement of Mozart Sonata K. 332. Certainly one can render a fast chromatic without a second thought, but that is far below the ideal of shaping a line, and drawing the listener to what beauty the composer has created. I believe that experimentation is a big component of practicing that leads the player to new revelations in an unfolding creative process.