Sleeping bags are often bulky to carry which is why a compression sack is really useful. Most sleeping bags come with a compression sack which allow you to stuff the bag into a smaller sack and then compress by tightening the straps.
If your going to a festival or backpacking it can be useful to have a second compression sack for your clothes. When backpacking saving place space in your backpack is really important, compressing your clothes can reduce the space your clothes take up by as much as a third.
You don’t even need to buy a sleeping bag to get your hands on another compression sack, shops like Millets and blacks sell the bags without the sleeping bag. An added bonus can also be the bag is waterproof which comes in handy in down pours or if you have to leave your bag outside.
So if your struggling to pack your clothes think about getting a compression sack.