While it definitely sounds like a good idea, every single time I've seen it applied, the reason was the opposite. It was essentially "we've got so little control over our stuff that we'd rather not touch". Mostly goes along with lack of backups, lack of change management, and lack of automated rebuild procedure.
If you have "danger times", then any unplanned disruption in that time will hurt so much more.
I agree with you, and I'm generally in favor of having 2 or more ways of doing critical things if possible, just pointing out the response which can have some merit.
If you know you have a major deliverable coming up, you can choose not to touch your git server until it's at a somewhat safe moment to do so.