These days the 4th round leads off day three of the draft. The third day of the draft is when the really good General Managers can separate themselves by finding great value. The draft hits triple digits at that point, with most teams having already selected three times, so you have to be good to land a star who had been passed over.
This year the Raiders ended up with three fourth round picks, giving them a better shot at landing a talented player. With those picks they landed edge rusher Maxx Crosby, cornerback Isaiah Johnson, and tight end Foster Moreau.