To avoid adding extra faces when you pivot about a parting line or parting surface, you can use the step draft option. For example, using the parting curve shown in the illustration, the step draft option adds a step where needed to keep the drafted faces intact.

Without step draft, some faces would be added.

With the perpendicular option, the step faces are created perpendicular to the draft face (A). With the taper option, the step faces are created tapered to the draft face (B).