However, there are plenty of ways to dress them up. Especially on beds with curves, the side rails can echo and complement the design. Structurally, the side rails connect the headboard and the footboard and support the mattress. This is accomplished most often with some sort of knockdown hardware so the bed doesn't have to be moved in one piece. The last major component of a bed is something to support the mattress.
Many beds have a box spring as well as a mattress.
Box springs are designed as a semi-rigid support. They can absorb some of the impact of a person sitting, lying, or even jumping on a bed, which prolongs the life of the mattress. Many people find the springy support of a box spring more comfortable than wooden mattress supports. From a bed builder's viewpoint, it is easier to build a wooden frame bed for a box spring. While a simple mattress needs slats or a platform to support it, a box spring is supported around the edges.