Unfortunately, not all your focus objects will be scantily clad. Sometimes this is a good thing and sometimes not, but not for the reasons you might be thinking.
Generally speaking, clothing reacts with the human body that’s inside of it and moves naturally with the flow of the clothed individual. Pants can be isolated the way that legs and shirts can be rotoed like arms. The same general principles apply across the board where humans and clothing are concerned. Overall, clothing doesn’t represent an overly tough focus object to isolate. It follows the laws of nature to the best of its ability and generally conforms to a consistent pattern of movement—generally speaking.
Like limbs, clothing will require more shapes around the joint ...