I'm not sure why this would improve the performance of the sub. I imagine that the sub will produce tighter bass if it is coupled rather than isolated from the floor.
But, I think that this may help reduce the amount of floor-borne vibration getting to your other components, esp if your floor is not super solid.
Anyway, this is all theoretical on my part. For $50, it is a cheap tweak.
If you already have something like Herbie's Tenderfeet you can probably stick one under each foot of your sub to see if it makes a difference.