Great drinking buddy because: "I'm not trying to honor you, I'm trying to get you to run my kingdom while I eat, drink, and whore my way into an early grave." That quote pretty much says it all. Robert is the Westerosi equivalent of your boy from back home who gets you in trouble every time you're in town. For two or three nights, it is amazing, but then you're like, "Dude, shouldn't you be running your kingdom."
Potential problems: Being peer-pressured into keg stands and shots. Enabling someone who clearly has a problem. Death by boar.