I like using mid-level devils as the brains behind humanoid villain groups. What's fun about confronting a devil is you know it's lawful. So it can be reasoned/bargained with, to a point. Makes for fun role-playing moments.
I never used them that much - more of a spice than a main course. I really liked what Dragon Age did - narrowed them down and gave them a solid theme (7 deadly sins). That would be more useful in play, IMO (players can get some understanding and familiarity instead of it being "another CE random collection of abilities from the Abyss" thing.