Super light and spray-proof ... for one
I had three straight days of cold rain on the Colorado Trail and was comfortable and dry inside the Silshelter. Because there is an effective "door" that closes (unlike a plain rectangular tarp), even blowing rain doesn't normally get in. There can be some condensation at times -- just pitch it a bit higher off the ground to allow more breeze.
Actually, there was one time I had water in the tent. But after some investigation I found that I had been sitting on my Platy bottle and had squirted out the water myself.
BTW, while this is technically big enough for two, with the sloping walls it's a tight fit when there's condensation. For one, this is a luxurious amount of room -- and still damned light.