Some plugins on wp.org just throws really unnecessary errors when wp_debug is enabled. For example, easyfancybox plugin I just tried gives an error "id is not set on line 351 etc etc." the error is author just checked if its true, not if its set.
Another one I use (Rich Tax Description Editor) throws many "undefined offset 1, undefined offset 2..." errors.
OK, I know they are not so important, unseen when WP_DEBUG is false but there should be some rules against this when publishing this kind of stuff or else coding becomes a different kind of poetry