ResourceLinks Control is it Aysnchronous and non blocking?

We recently completed a project were we used head.js so that we could load all the js Asynchronously and it woudnt block our page from executing, it works well, but i was just thinking if we actually needed to use something like that or if the resourceLinks control was infact non blocking aswell, does anyone have a clue, cant seem to find anything on it.

Thanks,
Rob