Even when i was a noob, playing mana hungry champs like Veigar/ Zilean i took it like a bi*** and didnt use Clarity i just never did.
Zilean (wait till chalice)
Veigar (get philo stone)

Sorry, Clarity is always gonna be worthless because Mana Potion and Total Biscuit of Rejuvenation exist. :/ running 9/0/21 on mages fixes a lot of mana issues. They dont need anything past the magic pen and Clarity could be something far more useful.

Clarity is intended for noobs and pre-level 30s who don't have runes and masteries or the skill to manage their mana. There's a reason it's never seen in normal games, let alone competitive games.

I've played it before. And Ignite is his primary choice. So I call bull on his prophecy. Clarity will not see (high-level) play. Pro players aren't right all the time.

do you even play AP Yi, just out of curiosity? cause like, he's diamond maining Yi and you're not :P

That same solomid guide also has wrong runes (scaling mana regen yellows) and masteries (Wanderer instead of Meditation).

Master Yi starts with 199 mana. Clarity restores 40% max mana. Now, you have two options:

1. Replace one of your summoner spell slots with Clarity and restore 40% mana once every 3 minutes, which (at level 1) results to 80 mana.
2. Be a normal person, put a useful summoner spell in that slot that actually keeps you alive, and restore 100 mana from your mana pot.

http://www.solomid.net/guides.php?g=46667-colzdude-masteryi-build-guide

"Clarity is the most unsung hero of this season. This is me calling it right now: Clarity will see play. If you want to remove your mana regen runes/masteries and take clarity instead. I can see this being incredibly viable. It makes it so resetting without blue is possible, gives you a great laning phase, and is super troll looking. Give it a try maybe."

just saying

Actually the other downvote was because he holds the complete opposite opinion. Just look at his guide.

Clarity isn't a viable pick because it takes up a valuable summoner slot, not because no one can make use of it. Of course a mana restore is going to be nice early game before you can build any notable sustain items. You can get a similar amount of sustain from just a Crystalline Flask, Faerie Charm and/or Mana Potions. There's no real reason to use Clarity over something like Ignite, Barrier, Teleport or Exhaust. And I certainly hope you don't mean to replace an escape spell with it.

Because the other vote was because he didnt want competition, this also makes sense, however I dont play ap mid so I dont use clarity :)

Did you just wake up on the wrong side or are you serious? I'd like some more info on what's wrong, thanks.

A Clarity guide which is not my guide? Instant -1, no questions asked!