A bed frame is an option structure that holds a mattress and bedding. A bed can be just a mattress and bedding on the floor. Raising a mattress has multiple potential advantages. For some people, it's easier to get into and out of a bed that's about chair height. It may reduce the pests that get into the bed. And underneath the bed, you now have some "hidden" space for storage. It's easier to make a bed that's at a higher height, and if it's not made, it looks less like a pile of dirty laundry when it's not on the floor. Some disadvantages are that the higher the bed, the more likely it is to hurt if one falls out, and the under the bed space is one more spot that can collect dust and dirt and require cleaning.