It isn't always sustainable, though. You do this long enough and a lot of people would start burning out. Certainly there are people who would thrive in an ongoing high-stress environment, but not everyone is built like that, or would want to stay in such a situation for long.
The occasional case of high stress, high productivity periods can be good for that feeling of accomplishment once the deadline is met. It's like the climactic ending of an action movie - a lot of activity leading up to a desired goal. However once the next chapter begins, you want to go back to a sense of normalcy, when people can recover and just relish the recent accomplishment.
Oh, yes, I agree completely, there is a need for peaks and troughs. What I learned last week however is that certain fairly mundane documentation and planning tasks can actually be completed in much less time than I have usually allocated to them (the domain is not IT or computing by the way).
The occasional case of high stress, high productivity periods can be good for that feeling of accomplishment once the deadline is met. It's like the climactic ending of an action movie - a lot of activity leading up to a desired goal. However once the next chapter begins, you want to go back to a sense of normalcy, when people can recover and just relish the recent accomplishment.