The peel ply material is generally used to allow the builder to have a "re-bondable" surface which requires no additional preparation once the peel ply is removed. That is very important, however, the peel ply serves other important functions as well. When applied over the wet lay-ups, you have a surface that will allow you to squeegee trapped air out without allowing the glass layers to move and shift around .  When the resin/fiberglass layup is cured and the peel ply is removed, the surface will be free of harmful sharp edges and spurs.

The resin surface normally will not totally cure when exposed to air which acts as an inhibitor. The peel ply  application will seal the surface and allow the resin to thoroughly cure. This complete curing of the resin surface is very important.   Later when sanding or grinding the surface, the "sticky stuff" will not be there to load up your sandpaper with uncured resin.