The Importance of Quick-cast
Ever wondered how to execute super-fast ward-jumping techniques and escapes? Or dodge an incoming Ziggs ultimate with your gap closer while standing in the middle? Well the simple answer is : Practice with Quick-cast. My gameplay dramatically improved once I set every ability to Quick-cast. ( Still bronze, though, and I'm not gonna complain ) The most difficult thing about Quick-cast is calculating skillshots, especially on champions where they matter ALOT. 
And the list of those champions continues on nearly forever. Some of the most important champions to have Quick-cast enabled on are Lee Sin, Orianna, LeBlanc, Katarina, Syndra (I hate Syndra without Quick-cast), and Rengar (for perfect pick potential). The most noticeable change is that it's faster to activate abilities because you don't have to click multiple times. Katarina legitimately becomes a moderately weak champion for low Elo without Quick-cast because your execution is shoddy when you cannot face-roll then ward-hop out.
I swear to all bronzies and low-Elo plebs like myself, we can win games easier if you execute things faster. As a person who commonly plays fast-execution champions like Katarina, Thresh, and Lee Sin, it peeves me to see someone slowly execute an InSec (Even if I can't do it), then get headbutted away by an Alistar straight into a flanking top-laner. Or for a Thresh to miss a Flay pick because he didn't keep them CC'ed by Flaying them towards himself during the second cast of Death Sentence. Or even a Katarina dying to a turret because their ward wasn't on Quick-cast nor Shunpo, so they took an extra turret shot and didn't even get the Shunpo damage reduction. I hate to admit that I don't like watching these things happen, but things sometimes need to be said.
In conclusion, that was my very general and probably slightly inaccurate opinion on the importance of Quick-cast. Anyways, thank you for reading my extremely long post, and I hope other low-Elo plebs (still like myself) take this into consideration.