work beyond the "normal" number of hours per week
may be paid or unpaid
PeopleWare says that ongoing significant overtime is unsustainable - you'll get the clock punched but with useless time. Extended overtime is a productivity-reduction technique, anyway. The extra hours are almost always more than offset by the negative side effects. This is true even if you don't consider the disruption of the team. When you take into account the way that the team members' differing abilities to work overtime tends to destroy teams, the case against it becomes persuasive. Most managers have at least a suspicion that overtime doesn't help, that projects that work a lot of overtime are not much of a credit to their managers' skills and talents. But they end up allowing or encouraging overtime, anyway. Why is this? Jerry Weinberg has an answer of sorts: He suggests that we don't work overtime so much as a way to get the work done on time as a way to shield ourselves from blame when the work inevitably doesn't get done on time.
Dec'2004 essay on OverTime at Electronic Arts (Computer Game) - The EA Mambo, paired with other giants such as Vivendi, Sony, and Microsoft, is rapidly either crushing or absorbing the vast majority of the business in game development. A few standalone studios that made their fortunes in previous eras - Blizzard, Bioware, and Id come to mind - manage to still survive, but 2004 saw the collapse of dozens of small game studios (SmallCo), no longer able to acquire contracts in the face of rapid and massive consolidation of game publishing companies. (Scale Vs Consolidation) This practice led to EA being sued by ex-employees, settling for $15M.
Steve McConnell's Rapid Development has a chapter on "Voluntary OverTime". Steve Maguire concludes that people who spend 12 hours a day at the office rarely actually work more than 8 hours, although he acknowledges that a self-motivated person will occasionally work more (Maguire 1994). Other experts have also concluded that you can't expect to average much more than eight hours per day (Metzger 1981, Mills in Metzger 1981, DeMarco and Lister 1987 (PeopleWare), Brady and DeMarco 1994).
cf Death March