As far as I know, BitKeeper does not seem to support the notion of "local" (intra-repository) branches.
Git supports these, and I've found them very useful. With Git, you can easily have debug/test branches without the overhead or config issues of an entirely different repo. I've even used one branch per bug so I can have several things in the air before merging them into the master branch.
The only way I can see to do this in BitKeeper is to have separate repos, which wastes disk space and adds the trouble of creating and managing separate directory trees in the file system.
To reduce file system waste, you can do a 'bk clone -l' which will create links instead of copying files and is fast.
Still, I find Git's notion of local branches to be a powerful tool when code wrangling.