You want to play slowly enough that you are just barely not making mistakes, and notice any mistake and practice that specific passage or figure until you can play it correctly. Maybe not everything needs to be perfect before you move on -- sometimes you want to build up an overall structure before filling in all the details -- but you will have to spend time unlearning mistakes if you just play the piece start to finish over and over again without paying attention to what you're really practicing.

My teachers never put it in such LW-y terms, but this is standard folk wisdom. This, and that mistakes aren't random, with practice decreasing the standard deviation of where your finger hits or something, but are instead usually the output of buggy mechanics. My teacher's teacher liked to say he's thankful for every mistake he makes, because it means that's one more mistake he never has to make again. A former LWer also wrote about this.