Rust is a vector for more rust. You want to remove it before it eats its way too deep into the metal.
I’ve seen a video of the same stacking technique using birchtbark instead of leather. The effect was gorgeous.
Ah, how about I not be lazy and find the link… https://www.youtube.com/watch?v=BLnqr6IGVgs Maybe it was another one I was thinking of, but this short movie shows it.
Rust gets on everything, and is hard to remove. If you are doing interior or finish work, a rusty hammer would leave stains on light colored wood, and also everywhere you set it down. Likewise any other tools it comes in contact with.
Rust is pure evil.
His vice restoration is also impressive (possibly linked from BB originally? Once you watch a few of these YouTube is very generous with the suggestions so it’s easy to lose track.)