One of my objectives with the Springbar tent was to keep it dry. The reason is not so much that I think it won’t be waterproof, but to not have to dry it out at home. To that end I put a tarp over the tent. And the ground tarp accomplished keeping it dry on the bottom. But it had another cool function, too - the tarp allowed me to easily position the tent in the best possible spot (level, no roots, etc.). It is much easier to move the tarp around to get the right spot, than it would be moving whole tent. Once the ground sheet is placed, it can also be used as a guide for placement of the tarp, which goes up next. All and all I found it invaluable. My only slight complaint: it did not easily go back into the bag. So rather than struggle, I just rolled it up and put a strap around it.