A standard mattress is meant to be paired with a box spring, with both items resting atop a bed frame. While you may be tempted to skip the frame for the sake of convenience or economy, resting a box spring on the floor may damage the box spring.
While you can place a mattress on the floor -- with or without a box spring beneath it -- the mattress may develop mold or mildew over time. All mattresses and box springs require airflow in order to stay dry; mattresses absorb sweat and body oils simply when you rest on them. During humid or damp conditions, mold and mildew may grow on surfaces that retain moisture, such as a mattress that retains moisture. A bed frame allows airflow beneath a box spring, keeping sleep conditions a bit more dry. If you do use a mattress on the floor, prop it up against a wall every week or so to allow the bottom to air out.
Wear and Tear
While you may feel more comfortable placing your mattress directly on the floor for the added firmness the floor provides, over time, the mattress will wear out prematurely. A box spring or bed foundation adjusts and distributes your body weight more evenly as you rest atop the mattress -- even more so with the support of a bed frame.
Protect the Warranty
Standard bed mattresses are designed to be paired with a matching box spring. If you use the mattress on the floor without a box spring, it may void the mattress warranty. Check the mattress tag or warranty card to familiarize yourself with the specific terms of the warranty.