What's the purpose of rehearsal (during lessons)?

Recently the idea of "rehearsal" has appeared in UK-based educational blogs. But there appears to be confusion. What's it for?

Here are some recent quotes:

🚨 Update: I've moved to a new home! You can read the newest, updated version of this article on my new website here: https://christianmooreanderson.com/whats-the-purpose-of-rehearsal-during-lessons/