Only use them during repairs and upgrades
The servicablity factor the moon offers gives it some big pluses for telescopes. I think there should be deep space based telescopes as well but most likely when they die they can't be fixed, at least not quicly and easily, as would be the case with moon based telescopes located near a lunar base.
It's great to be discussing this realistically! A year ago this would have been a purely academic discussion.