Sand paper has changed over the years. I am not familiar with the details but understand that at least one brand or type has stearate coating to make it self-lubricating.
Years ago, I picked up a box of miscellany at an auction that had a 3" tall stack of sand paper. The grit was loose on the surface and some would fall off when holding the sheet vertical.
If the abrasive is not lost to the surface being sanded, where does it go? Some or all could be in the dust but if it comes loose, it seems likely some parts could remain imbedded in the surface.
Rustic? Well, no. That was not my intention!