agreed, in significant amounts to color the resin it's like sanding concrete but in very small amounts that are just enough to increase the viscosity a little,,enough to take a thin epoxy like MAS it doesn't make sanding that much harder,,,of course the slight increase in viscosity isn't that much of a benefit compared to another coat but it's like cooking ,,"just a little" can work. I've seen a Cape Charles sitting in the rafters of a boat building school for a couple yrs, they used A LOT of cabosil as a fairing compound for some reason....there it sat abandoned after a few attempts of sanding.