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.
There are primarily two types of sleeping bags. One is the mommy bag and the various other is the "traditional" rectangle-shaped resting bag. Currently mind you, ain't nothing incorrect with old school in any way. It might be your preference once you uncover just what it's like verses the mommy bag.
Goose Down Resting Bag: There's nothing with a greater weight to warmth proportion when compared with down. A Goose Down resting bag is extremely light-weight. Down is only for people most diligent in maintaining their sleeping bag completely dry. Hood: as detailed previously with the Mummy Sleeping Bag, a hood having a drawstring could assist keep temperature.