It is designed to be set up as an A-frame. You don't have to carry any tent poles but can use trees, branches or hiking poles as support on both ends. It is also resistant to tear and blunt puncture. It also keeps your sleeping bag or blanket clean and prevents you from rolling off in the middle of the night. Finally, it serves as a storage space.
Most sacks are way too heavy for their intended function.
I've cut the weight drastically by using lightweight nylon which is strong and water resistant. For 1-3 days' worth of food, the large bag is fine. For trips over 3 days, put your food in the extra-large sack. The side you're laying on is not providing much warmth because the insulation is crushed and compressed. The blanket design solves this problem by surrounding your body with thick insulating loft on your top and sides while your foam pad warms your bottom side.