When we back out a package, there could still be some lingering objects in the lower test regions.
We use 3 sites as parallel streams and sometimes users can start in the wrong stream/site, thus leaving objects around.
We always recommend fixing forward, that is creating a package with the -1 version of each object in the package you want to back out, just for this reason of keeping all the lower regions clean.
It would be nice to have a flag or choice as to when you really want to use this.