I recall some US gov agency, possibly the IRS of all things, that would only accept forms being submitted during US working hours. Because the computers also need time off I guess?
In some cases I know (with smaller orgs) it happens because someone put a requirement in that they need to react to incidents with the service within X hours, but didn't provide the budget for the employees or external service needed to have that 24/7.
I've heard of similar things being done for ADA compliance. Something about requiring a phone line to be up at all the same times as the website so instead of a 24/7 call center you just turn the site off.
