Often times when tracking a shot, it's helpful to start in the middle, or the end, and work backwards. I currently have a shot that I need to use rotobrush on and I can see this method of work backwards saving a lot of headache. Is it possible to run rotobrush in reverse?
Roto Brush isn't as intuitive as it might seem. Check out these resources: Roto Brush in After Effects
For example, if you're not freezing your Roto Brush work when you're done, you're really screwing yourself.
The resources linked there explain propagating forward and backward (as you asked), freezing, and much more.