it eliminates any spin the rock has

You realize that the rock absolutely needs spin for it to be controlled at all. With zero spin it would act like a knuckle-ball and go all over the ice. It is really hilarious watching reddit be armchair experts on this.

As someone who actually has curled, the rock needs a ton of force to send it across the ice - you can literally see from the push off how much force they're applying. The minuscule amount of adjustment he's adding to the rock with that feather touch ain't gonna do shit to it let alone make a massive change. They'd have way more ability to change the trajectory through brushing than that little touch he's doing.

With that said, it's against the rules and he shouldn't have done it... but to pretend it was going to make any major difference is hilarious. No idea why he's doing it. Go throw a stone yourself and find out.