I do store some sleeping bags for long periods of time compressed. You just have to know what you are doing. For example, every fall, as winter approaches, I take one of my cheap synthetic bags, stuff it, and throw one into each of three commonly used cars. (Neither the hot rod or custom truck.) The bags stay in the trunks until spring approaches. These are cheap bags ($50 and less). They will degrade and have to be replaced every 5 years or so. They are only for an emergency, to save one's life. I know what I am doing, (destroying the sleeping bag), and I accept it. I retire the old bags to house duty or give them away.
My good bags get better treatment. I hang the expensive 800 fill bags ($250 to $400), and I lay the better synthetic bags out. Some down bags out there run upward of $800. Take care of your gear, and it will take care of you.