The trade-in values can vary wildly and are usually disappointing. But sometimes they are higher than what you'd get for a device anywhere else and that's why I actually used it once, in mid 2020, where the values for Intel Macs were high compared to the much lower brand-new-M1 pricing. Sold the Intel Mac instantly when I noticed it and bought a faster quieter M1 for the same money (around 1299, though I did have less storage with the M1 model, but that was a good tradeoff).
I even got to keep the USB-C power adapter that came with that Intel Mac, so now I use that second charger in the office. And Apple had a courier pick up the Intel Macbook for free saving me a trip to the post office. Confirmed they got it around 3 days later and had the money another few days later, it was really quick with no further interaction required from me.
Now the prices they offer are so low it's ridiculous. For a recent device that's even still within Applecare they offer 1k when it cost 5k brand new. I bet it would be back in the refurbished store for multiple times the offered price. Still, I'd always check that pricing just in case.