As I understand it, any API call using the deprecated authentication scheme will fail for the 3-hour period, not just logins.
So for some folks, maybe CI will be broken, or deployment automation, or even code review.
The trade-off here is to be disruptive enough that folks will notice and fix old callers of the API, while not leaving thousands of coders permanently in the lurch (they'll notice and complain, but three hours later they can get back to work, while someone fixes the infrastructure in the meantime).
So for some folks, maybe CI will be broken, or deployment automation, or even code review.
The trade-off here is to be disruptive enough that folks will notice and fix old callers of the API, while not leaving thousands of coders permanently in the lurch (they'll notice and complain, but three hours later they can get back to work, while someone fixes the infrastructure in the meantime).