I just acquired a spinnaker cloth groundsheet with a used tarp. I cannot figure why one would use the groundsheet. If I'm sleeping on a pad, the groundsheet won't keep me any drier. If I lay my rainwear and backpack down under my pad, the groundsheet won't keep the pad any more protected or dry. Who finds these essential, and why? I'm thinking of cutting it up to make stuff sacks or something. Please enlighten me!