In 1917 the zipper was developed and, of course, these made for a terrific seal for the rectangular sleeping bags allowing an individuals body warmth to remain trapped longer consequently keeping them warmer on those cold winter season evenings. Basically the term resting bag essentially suggests a safety bag for someone to rest in.
The other sacrifice is the size or thickness of the bag. A mummy sleeping bag essentially will certainly be much smaller sized for bring around which is why it is a preference for many backpackers/hikers. The rectangular resting bag isn't as small yet because it's not common to be lugging it, apart from somewhere in a vehicle while getting to your intended location, the bulkiness of the bag is not as large a problem.
The definition of a sleeping bag is a protective bag for an individual to sleep in. Some people may not like the feel of sleeping in a normal rectangle-shaped shaped bag, choosing the closeness of a conical one, whereas others could feel too claustrophobic. Camping resting bags are a lot more compared to simply resting bags. They are the determining factor of whether your outdoor camping trip is an enjoyable one.