I naturally developed this as a key technique when I interview software engineers. Repeating back a long-winded technical explanation servers several purposes:

* Makes sure you indeed understood what you think you did.

* Gives you some time to think what to ask next.

* Focuses the conversation.

I think the last point is also key. Usually these kind of explanations take several minutes and can ramble a bit. By repeating something back clearly and concisely you can focus the conversation on the point that you want to dig in further.

Of course this technique is also excellent while collaborating with colleagues.