It's ok to overlap sometimes, depends on the situation. If you are in a line where it's strung out, not a good idea because the rider ahead of you has the ability to go side to side and hit your wheel. On the other hand, if you are in a pack and the rider in front cannot move to the side due to being in a sandwich between two other riders thus no allowing him to move, it's ok to do it for a little bit, just don't do it too long and especially when you are coming up on a turn.