Why need a delay between readings?
Those delays are nonsense. They don't add to the stability of anything. The best you could say is that they stop you spamming your serial port. (However 1 ms is not very long).

Sometimes people throw in a delay because "it seems to work better" without examining the underlying cause. I would speculate that in this case the author may have been using delays to improve receiving serial data, and got the idea into their head that the occasional delay now and then "improves stability".