It depends on how bad the pivot is as too how much material is removed and then how much free play you then have in the pivot hole. The actual process of polishing a pivot in good condition will remove almost no material. If you have a good straight pivot with just a touch of scoring and the pivot hole isnt worn then no, under a normal polish it would not need re-bushing but quite often you will find by the time you have polished the pivot back to good working condition it could well need bushing as the pivot hole would also have wear in it from where the clock has been running.
Hope that makes sense?
Paul.