It is possible to use your entire forearm against one of those giant sloping holds where there's basically nothing to grab its just an awkward orb bigger than your head and you're praying to the gods of friction to keep you there. You do get a lot of friction, laying an entire forearm on it! So much that, after moving your feet up, you're in a terribly awkward position with no good way to move your forearm without losing a bunch of skin or falling off the wall.
I'm better at sloper holds than I think I am, but, confidence & lack thereof adds its own difficulty.