> it was a false economy - if we'd just worked normal hours ... we could have achieved the same result, without all the mess along the way.

Nearly 100% of the time I was on teams that grinded down to the bone, things turned out poorly.

Nearly 100% of the time I was on teams that have tons of slack time, we absolutely crush it. If you're "busy" all the time you can't reflect, put things in perspective, consider alternatives, etc. It is, exactly as you say, a false economy (probably a better term than work theater, which implies slacking off, which is not what I meant)