I don't think I was ever able to straight copy and paste from SO, everything needs adaptation, and code can often be simplified. And you need to understand your code. SO was useful, but nothing could be used copy pasted.

Maybe this is not the case if you are doing a dozen throwaway websites, but for anything serious that is an absolute requirement. I work in hard realtime safety critical code, think things like brake controllers, medical devices, auto pilots, etc. In my case industrial control systems. You need to have full control and documentation for your development process.