it groups the branch into a chain of commits, and has dependancies between them, so you can approve a commit on top of the chain, but it will not merge until the ones it is based off merge.
My recollection was that you had to give each commit its own local branch name and both rebase and push them one-at-a-time with Gerrit. Are you saying that an entire branch of commits can be pushed and updated at one time?
yeah - at least with something like git-review [1] when you do git review on a branch with multiple commits, it creates a chain of commits in gerrit with one command.
