The futon frame is a very basic structure that is similar to a hinge. Futons usually have a metal binding hinge that holds the back of the futon upright when the futon is in the couch position. When you pull up on the back of the futon frame and push down, it releases the hinge from the binding point and allows the futon to lay flat for the bed position. As the futon itself isn't the most expensive, the hinge isn't the highest quality either. Over time the strength of the hinge weakens and can barely support the frame to stand upright in the couch position. At this point you will have to lean the futon against the wall to make it stay in the couch position. You can order a futon hinge, but installation is very difficult and the hinge almost costs as much as a new futon. Once the frame hinge is broken, you can either keep the futon in the flat bed position at all times or just throw the futon frame away.
If you always keep a cover on your futon you will be able to extend the life of your futon mattress. Even if you have the futon mattress covered, spills and body odor will begin to soak into the futon. Spills and body odor cause bacteria to build up deep in the mattress which over time won't be able to be washed off the surface. Also with the constant bending of your futon mattress from the couch to flat bed position, the springs will eventually wear through the futon mattress fabric and they will poke you. If either of these scenarios happen it is time to throw away your futon mattress.