You don’t have to have had a disaster like mine to need sandpaper while finishing a painting. Many artists use sandpaper to remove heavy blobs or brushmarks from their painting. It’s a matter of taste. If you like a super-smooth, super-finished look to your work, you probably have to pull out the sandpaper. Most clients like to see brushwork. It’s a big signal that you are not buying a giclee, although I am told that many giclees have an artist finish the giclee with some brushstrokes to get rid of that computer finish.
Before you break out the superfine garnet sandpaper, make sure the paint is super dry. If you don’t you’ll have a dandy mess on your hands. The paintings that were damaged at my house are hardening in the cool house and I will wait a few days before I try to remove the dust covers. Hopefully when I pull them away, the damage will be limited to the varnish. In that case, careful removal of the varnish and refinishing the painting should be all that is necessary.