When you chair stays in one place for any length of time it creates grooves where the wheels are. So it's just as hard to get out of those groves as it is rolling your chair along the carpet that the mat is on top of.
I purchased this to go on top of the carpet in my office and it does work but it is thin. I would go for the next one up if I were to purchase one again.
The "Staples® Flat Pile Carpet Chair Mat 36" x 48" Lip" isn't a great fit for the L-shaped desk I have. It fits just right up against the sides of the desk so I can't go a size larger; however the lip isn't wide enough and the front right wheel tends to fall off. I also find that if I roll too far away from the center of the desk the back wheel falls off the mat. If I had the keyboard installed in the corner of the L-shaped desk this would not work at all. However it works sufficiently since the keyboard is located facing forward.