If you got an Enlightened quilt, it should come with four straps, of which you can use either set, or none at all.

The longer, non-stretchy strap can be used to secure your quilt to the sleeping pad, while the shorter, stretchy one just fastens it around you, hopefully stopping drafts.

I've never found the need to use them, but I did intentionally get a wide quilt, even though I'm not to wide of a person, which gives me more than enough stuff to wrap around me.