Branch rescheduling has 2 main scenarios:
1.) Reschedule all dates within the selected item based on a shift in start date or due date. For example: right click a milestone >> branch rescheduling >> shift out the due date two weeks >> all subitems in that milestone will shift two weeks, regardless if dependencies or manual dates are used.
2.) Clear out all of the manually set dates in a slice of the project
I would recommend hopping on one of our Q&A webinars to see it in action.