format-patch usage

Hi all,

Two questions from a git neophyte about using format-patch:

First, what's the point of adding the Signed-off-by footer, if you're
the author of the patch? I can see the utility of the committer adding
this, as a record of who committed it, but if you wrote a patch and are
submitting it to the list, then you've presumably "signed off", haven't
you? Or is there some subtle distinction between exploratory patches and
"real" patches being made?

Second, it seems like commentary about a patch can be placed after the
"---" but before the "diff --git" lines. Is that correct? Is that
accepted practice? It seems a little backwards to have the commit
message first, then the commentary. Am I correct in assuming that
git-apply ignores anything between those two lines, including the diff
stat, and so that's the reason people put it there?

Thanks,

-- 
William [off-list ref]