Regardless of the material used to make it, a drum mat is a must-have for studio and performing drummers alike. A piece of old carpet may serve as a budget mat, but there are numerous types produced exclusively for the purpose of laying underneath a drum set. A drum mat is a piece of material–usually rubber or with a rubber-coated underside–that rolls out and on top of which a drum set goes. They come in different shapes and sizes, but there are 2 basic reasons drummers use them.
Non-Slippage of Drum Set
Most drummers, at one point in their performing or studio career, have made the mistake of not using a drum mat. What they likely found out (the hard way) was that their drum set tended to slide away from them as they played. Especially when performing and your energy is high, it doesn't take much to send the bass drum moving. Pretty soon, you can't reach the pedal, and you'll look quite silly.
While this is not nearly as important as preventing a drum set from sliding away, a thick, rubber drum mat can help to absorb some of the noise when playing. This is more important when playing at home for rehearsal, but it's still a good reason to buy a quality drum mat.