I've yet to work on a game project that didn't involve some amount of crunch near the end, so I'm not here to talk about how it's avoidable...even though I do think it can be :) I am a firm believer that an employee's effectiveness during crunch hours drops dramatically and have seen many times that a 12 hour day can be much less productive than 8 solid hours.
The thing I've learned about myself over many years of working on various projects is that if I don't get some breaks in the crunch...I will begin to get sick. Once early in my career, I worked my self so ragged that I got Mono and that was no fun at all. On the Simpsons Game we were working toward our first playable level which I was building. I was on a really tight deadline and ended up getting so sick that I was taking naps on the couch at work in between builds so I could get some rest. My illness actually wiped out nearly the entire team...how's that for decrease in productivity? I even got an award for it!