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.
If you see a +20 degree score that would certainly indicate that the bag should be cozy enough for temperatures that are 20 levels or warmer.. And if you see a - 20 level score then it has actually been figured out that the bag needs to be cozy sufficient for minus 20 degree climate.
Because of the cuts of the two bags and also the space they supply you might discover that you're on your back sleeping in the mommy bag while the rectangle-shaped bag will certainly let you sleep on your side, tummy or back. And also depending on exactly how large the rectangular bag is you can change your body right into also one of the most one-of-a-kind but typical for you resting settings in order to get a comfy night's remainder.