I don't see it often, and when I do someone always asks them to not take it. I can think of plenty of applications for it. A versatile support doesn't always have to take something like Exhaust/Flash or Heal/Flash. CV comes up ever minute. I recognize there are a lot of scenarios where it's just not optimal, but it's definitely not a wasted summoner. CV/Exhaust could be really good on a support who buys Mobi boots. Or Smite/CV on a jungler who can run away like Olaf. Shen split push would be super safe with it, and he could ult away instead of flashing if he really needs to, or dash through walls. Not saying CV is the best or anything; just that it's good in its own right.