I always have drinks whenever I'm on long-haul 5 hrs+. It just makes the flight easier to endure, and not just cause it's free.

Depending on the FA though, they might cut you off if they think you don't seem to be able to hold your drink. I once finished 2 bottles of wine on a 8 hrs flight, and the FA just smiled and complimented me on my ability to drink. Another time the FA cut me off at 2 beers! Whenever I get drunk, I just knock out and fall asleep. Even when I am out partying, my friends would complain that I'm wasting perfectly good alcohol and should just take a sleeping pill instead! lol