Smite top.

Depends on the champion.

It's REALLY good on Shyvana. Cinderhulk is really good on her, and Skirmisher's lets her deal absurd amount of damage while taking virtually none while in dragon form. It's good on her because Burnout and her ult allow her to escape ganks without the benefit of Flash.

It's not really used on many other champions, but in theory, it should be good on champions like Shen, Renekton, maybe Gnar, maybe Vladimir, because they have ways to escape ganks too.

It was taken into pro play because it was done in solo Q. Does that answer your question?

It works well on voli and Naut as well

Cinderhulk, imo, is only good if you'll actually buy HP items, so it's not good on every top laner.

But as for taking smite? Depends. Taking the first camp for an xp advantage isn't terrible (just let your friendly jungler know, they shouldn't care if it's the last camp in their route and it'll respawn by the time they get to it), it'll let you last hit cannon minions even if you're being zoned due to its range, and whatever smite you choose isn't terrible either. Challenger smite especially can piss off many a Riven player, especially if you play something like Teemo.

works great on people like sion or zac or voli it's a niche pick. If you use it for any other enchantment than cinderhulk then nah