What about smart casting

Yes x3

It is better. There are only a few spells in the game (namely vector spells like Viktor's E) that are easier/more intuitive without the smart casting. It takes a little adjustment when you first start smart casting but you get use to it quickly.

I dont know, I rarely use them for non-targeted abilites, it just feels weird to me, but they should definitely be more efficient since you have to click twice as many times if you dont use smartcast. Depends on whether you like it or not. But for targeted abilites definitely use it 100%

I love using smartcast.. I am amazed how long I played league w/o using it. Definitely a quality of life improvement. I normally don't use it on champs that have charge up abilities. So just be sure to turn it off on Xerath's Q, Varus Q, etc..

Depends. I personally dont use it (bronze trash who needs it to aim and know ranges LUL). But on champions with spammable abilities, or certain point and clicks, it can work better.

I could count on one hand the skills I wouldn't necessarily want on quick cast and I think honestly Viktor probably holds two (his e and debatable, his r).

It's insanely useful for champions like Ezreal or Urgot.