I keep newspaper under the driver's floor mat to absorb any moisture that spills over from the floor mat. If the newspaper is changed frequently enough (every few days), it keeps the floor dry.
On every vehicle I have owned, the floor boards have rotted out. My truck is now ten years old and I plan on keeping it for another seven or eight years and I would like the floor boards to stay intact while I have the truck. Keeping the floor dry should help.
Of course those who do not live in a snowy area might not necessarily appreciate the effort needed to keep a vehicle from succumbing to rust.