This is only true if you use format-patch?
I believe you need to use git-am(1) to get the metadata (author, timestamps, et cetera) applied.
Shouldn't git-am(1) be mentioned for git-format-patch?
"Where foo is replaced with the first line of the commit message."
I'd suggest that "Once the patch is accepted upstream" here. There's no harm in keeping branches around and it's a pain in the butt to try to reconstruct the branch from the hashes in the diffs (which aren't the commit hash, but the object hash).