I agree that having rotations in outside clinics can be beneficial especially for building up speed, however the caveat is that the quality of externship sites can vary alot. If you are at a good site with doctors that are eager to mentor you and allow you do to do a variety of procedures including endo, removable prosth, surgical ext's then it can be very beneficial. However, I've heard of students who are stuck at externship sites where they are limited to simple fillings, doing alot of hygiene without an assistant assigned to them and not allowed to do more complicated procedures since the doctors are too busy seeing their own patients.