I am pretty high functioning. I only drink after work (work nights) and don't drink enough to get hungover for my next shift.
With that said, I think I half ass it a lot of the time to get out on time, because drinking is on my mind. It's not even a conscious thought sometimes, I think my body and mind are craving it and I subconsciously end up rushing through my work to get home and start the process of 'unwinding' (aka drinking until I pass out.)
I never have missed shifts over it at this job. Mind you, four years ago when I had my first phase of heavy drinking, I missed several shifts at another restaurant and was let go. Not a good feeling.