I think it goes without saying that absolutist views on work are going to be wrong. If you structure your organization around a work/life balance, you have to been more strategic about how time is used than an 80hr/week "burn-and-churn" organization. The upside is you'll have less turn-over, happier employees, and (hopefully) happier customers.

I'll just say there's one hidden advantage to less crazy hours: it's a lot easier to spot mediocrity and weak-points in processes and teams. I'm not talking about people skill-building for the first time, but if someone consistently needs to work twice as long to get the same output of their peers, there really shouldn't be a social incentive structure in place to reward them for what is effectively poor performance papered over with extra hours.