Crowns are cemented on the tooth. It needs a lot of friction to allow it to stay in place. As you can notice, using course burs will leave a streaky rough interface behind on the surface of the prepared crown. These “streaks” interface provides the friction and a lot of surface area in which the cement could attach to. If you are polishing the surface, it has no benefit at all, you actually are promoting for the crown to slip off because you already removed the grip (or the friction) that the streaky interface was supposed to provide for.