With a “branch” you’re often talking about the same repository (as in you can push to the same repository). With “forks” there might be N different “trees” wher

With a “branch” you’re often talking about the same repository (as in you can push to the same repository). With “forks” there might be N different “trees” where each tree is “mine” and the coordination could be patches via emails. With such a loose relation you could easily end up in a situation where you are conceptually “force pushing”. Because you might use the same patches but not have the same graph topology. What if you send three patches to the upstream and they incorporate it with git-am(1)? Then they have effectively made a different history with your patches: three commits which are not the same as your three but may be patch-identical. Then you need to keep track of that “force push” by the upstream so that you don’t maintain your now duplicate commits (as in distinct commits but the changes are duplicates).