If you remember Three Dog Night, in actual life that's a cold enough night that a shepherd would need to curl up with three dogs to keep warm!

Some like deliberately to use a less warm sleeping bag and regularly use insulating clothing for cold temperatures. I like to have my sleeping bag warm enough for normal conditions, and my insulating clothing as a reserve for when its's unusually cold at night. As suggested in my above post, occasionally I've needed that extra margin of warmth!