Wet sanding produces no airborne dust and thus eliminates the need for a dust mask or respirator. The sanding residue is easily removed from the surface with a damp sponge and you and the rest of your boat and workspace remain clean. Wet sanding is faster cutting and much more sandpaper efficient than dry sanding. As a general rule, finer grit paper should be used when wet sanding as opposed to dry sanding and care should be taken to make sure the sanded surface is completely dry before applying the new finish material. Disposable latex gloves protect the hands from abrasion.
Paper is cheap so buy the best.
I use 220 grit for build-up sanding coats on varnish or paint and 320 grit for the final coat. This makes an excellent sanding pad that is easy to hold and to control the amount of moisture on the sanding surface. Dip the sanding pad in a bucket of water, squeeze out some of the water and begin sanding about one square foot of surface at a time. Sand with the wood grain. After a short period of sanding, you will begin to notice sanding residue on the wet surface, indicating that you have broken through the old surface gloss.