I gave the rogue Advantage twice. The first time was when he went down fighting the ogre and received a Cure Light immediately after. Things shifted so much that the rogue went from being right in front of the ogre to being right behind (out of sight, out of mind). Rather than standing up, announcing his return to the fight, then attacking, he decided to hamstring then stand. I applied a -2 penalty for melee from prone but also gave him Advantage.
The second time was a couple rounds later when he got sick of the three goblins lobbing arrows at him and the cleric. He spun on a dime, charged, and threw his knife. I ruled that it was such a dramatic shift in tactics that the goblins were somewhat put off by it. I may have made a Wisdom check, but I don't recall.
Overall, I really, really, freaking love the Advantage/Disadvantage system. It's a snazzy mechanic that I can freely DMO for creative players without being stuck by detailed rules that may not make sense for a given situation. It has enough potential (instant redo!) to make players feel like they got a real bonus without being powerful enough to make me worry about handing it out too often. As illustrated in my first example, you can have Advantage and a penalty, at the same time. Go ahead and be creative, guys -- if you're clever, I'll throw you a bone.