Sometimes you have to crunch and work overtime. This can give you a productivity boost and help you get important projects over the line. However, studies show that doing this in the long term — past four weeks — can actually make us accomplish less.
The graph above is from Daniel Cook's Rules of Productivity presentation posted on his Lostgarden blog. It shows how working 60 hours a week leads to a productivity deficit or slump — one which you'll have to recover from. He writes:
In a 60 hour crunch people have a vague sense that they are doing worse, but never think that they should stop crunching. They imagine that working 40 hours a week will decrease their productivity. In fact, it will let them rest and increase their productivity. This behaviour is fascinating to observe. Zombies stumble over to their desk every morning. Temper flare. Bugs pour in. Yet to turn back would be a betrayal.