I haven't, but I read a grow the other day where the guy did. He used it under his coco slabs so that when the roots poked out under the slabs they went right into the matt so that they wouldn't have a chance to be exposed to light and to keep a little extra moisture in the tray. He says he uses it all the time now. He also said that there are two different sizes of thickness and he said that he uses the thinner because it worked just fine and was less expensive.
Hope this helps some.
Adieu