The fine sandpaper used for wet/dry finish sanding, 220, 400, 600 ... uses a grit of carbide which is really hard and sharp. I see people do that thing where they fold sandpaper over a string and then free stroke, and it makes me wince!!
The grit itself is WAY stronger than the cheap bonding agent used to glue it to the backing, and this type of sandpaper quickly loses it's effectiveness when the grit gets knocked off. Do you really want that happening over the soundboard, or anywhere near the sound hole of your precious guitar??? What do you think happens the next time you lovingly wipe down your finish with a gentle microfiber cloth and there's a dust of carbide grit getting caught up in the cloth? Maybe my imagination is too intense... A lot of people who know what they're doing seem to do this, but I never will.
I still use fine wet/dry paper (600 grit), just nowhere near my guitar. I hit the backing with a quick spray of adhesive and tack it to a tongue depressor, then trim it to make a custom fine grit file.
"If I have seen further it is by standing on the shoulders of giants." -Sir Isaac Newton
Armin Hanika 56PF