[danielweber]

It definitely depends on the field.

Plus, in certain fields, even if you are experiencing diminishing returns, you can still squeeze more value out of those additional hours than someone else can.

Imagine one Friday your company calls the law firm you have on retainer. The guy handling your case has already put in 50 hours this week and is only operating at 80% capacity. You are still going to get better work out of him than his coworker, because your guy has everything about your case stored in his head without reading any notes.

On the other hand, if someone was on some type of monitoring duty, where usually nothing happens but if something does happen it's very important that he make the right call (ie guard duty, nuclear power plant operator) I would want to split his work over many people.

Sometimes two 30-hour workers perform better than one 60-hour worker, and sometimes they perform worse.