Well, for new developers they might not put together "we use this calling convention" with "and that means you can find things like self, _cmd, or the exception

Well, for new developers they might not put together "we use this calling convention" with "and that means you can find things like self, _cmd, or the exception that was thrown in these registers ... which can ease debugging your app". That's useful information I wish they'd put up in their docs, is all.