Raising the mattress off the floor with a box spring not only increases your comfort, it improves the look of the bedroom when you don't have a slatted bed frame. Once the mattress is raised on a box spring -- and set into a low metal frame with wheels or on feet screwed into the wooden frame -- you only need to place it against a headboard for the finished look of a bed. Also, when you buy a mattress, not buying the compatible box spring manufactured for that mattress can void the warranty on your pricey purchase. And while mattresses are expected to last at least seven years, using a box spring can extend the useful life of its accompanying mattress, according to the mattress industry's Better Sleep Council.