You can never be too prepared, right? Well…let me put it another way.
Have you ever over prepared a piece of music? Most people would say, no. But where do you draw the distinction between, “I can finally play through this piece without any mistakes!” and “I would rather [insert something gross here] before playing this piece again.” For some reason, musicians have this obsessiveness with perfection (we like to get all the notes right). We can always find something to polish in a piece of music long after we’ve learned it. Which isn’t necessarily a bad thing, but I think the trick is to know when to stop polishing a piece and move on to a new one.