It's the highest signal question to ask in reference checks as well. It gives the reference an out to be honest and not feel like they're being disloyal. It's a very direct question that is hard to fudge without lying.

"I would rehire them in a heartbeat" = yes, "I have been trying to recruit them for months, you lucky bastard" = yes, "If the right role came up, I would certainly consider them" = no, "Uh.. yeah, I think" = no