But that doesn't really make sense? Lets say that Facebook need 100 engineers with said skill, would they open up 100 PERM positions and if any of them are not

But that doesn't really make sense? Lets say that Facebook need 100 engineers with said skill, would they open up 100 PERM positions and if any of them are not filled they can keep the worker? Otherwise what if a candidate applies to the PERM position and not the normal ones, while the temp worker would be qualified for many other positions advertised by Facebook that goes unfilled? The whole system seems very badly thought out to be honest. And no, just because you need 100 of something doesn't mean that it isn't highly skilled. People who can architect highly performant reliant systems are not that common and can fit most spots at Facebook, they need thousands of those.