I've never had this much fun on support before, the pressure you can put on the enemy is insanely good. I can tower dive easily and pick off any champs and my Q isn't blocked by minions like on Nautilus, Thresh or Blitzcrank. No one anticipates Vi to be a tanky support either and she's slippery as hell because of her Q escape, so the survivability is very good. In team fights she absolutely shines with her Q and R of course, making it easy to pick off an ADC.