In merge jobs, buffer C is not deleted here, but rather according to
ediff-quit-merge-hook.
ASK non-nil means ask the user whether to keep each unmodified buffer, unless
-KEEP-VARIANTS is non-nil, in which case buffers are killed unconditionally.
+KEEP-VARIANTS is non-nil, in which case buffers are never killed.
A side effect of cleaning up may be that you should be careful when comparing
the same buffer in two separate Ediff sessions: quitting one of them might
delete this buffer in another session as well."