How Do People Use Quick Cast?

I usually don't use quick cast (or smart cast I don't know the difference) and I've grown used to it. People keep on saying that quick cast is really useful and that you should use it. But whenever I try to use quick cast it seems too fast (I know it's called quick cast for a reason but it's still too fast for my liking) and I miss my skillshots because I don't expect it to go immediately, I can use point and clicks fine but the skillshots are too difficult for me to use quick cast on. So how do people use quick cast on all of their abilities? I have to keep on changing quick cast on and off whether I feel like it'll help me or not.