I'm not a heavy person and after using the floor mat for the first time I noticed that the castors on my chair caused an indentation on the mat. Now whenever I sit at my computer I roll into that spot. My old floor mat of more than 20 years never had that problem.
I put this mat on a short pile carpet and put my office chair on it. The chair immediately sunk into the plastic mat. I only weigh 152 pounds and the chair has 5 wheels on it. The indentations were noticeable and did not go away.