User blog comment:Andrew.heo1/When to Get a 3rd GP10 Item on a Support?/@comment-76.187.209.68-20120815030803

You only buy the 3rd item if you're ahead in terms of gold. That rule applies with junglers as well (which I heard it's optimal to get your 3rd one by 11-12 minutes if you're a jungler so I'm only taking a wild guess)