If you are backpacking, space and weight is paramount. And, packing gear that serves multiple purposes saves on both. We have all likely been hunting in paces that required a lot of walking. The kind that gets you hot. So, you wear minimum clothes while walking or humping in and, pack outer layers for when setting. For me, a primaloft vest, a primaloft liner jacket, wool or microtex button up, and a baselayer will get me to 20 or so on sunny days. I can leave the vest out and use the woobie when setting awaiting the next move or waiting on an animal. I can use the same woobie when lounging in the evening before bed. I can use the same woobie for a blanket over my top quilt when ground sleeping in single digits. Or, stuff it in between my under quilt on my hammock when it drops to the low teens. It's just a multiple purpose piece of gear. My homemade one compress very small. As small as the vest. It's light because I made it shorter and, out of a lighter shell material. And, the big thing is, I could wear the vest for everything I can use the woobie for. Except sleeping. I don't like bulk when sleeping and the vest doesn't boost the whole quilt like the woobie.
If I had a bag that was almost good enough, instead of buying another $400 plus bag, I'd buy $50 worth of material and sew one or, have a local shop sew me one for using when sleeping. God Bless