It’s inportant to recognise that all overtime has a cost (both to you and the business). If I crunch this week, I typically lose more than I gained next week. I believe that Peopleware has a section on this.

Basically this means that crunch is fine to get out of a pinch, as long as it’s very infrequent and the cost is allowed for. Eg if there is an important deadline due this week, by all means, crunch to meet it, but next week is going to be unproductive and these tight deadlines cannot he a regular thing.