We used to used a scrap of carpet for a few indoor shows where floor covering was required. Personally we found it to be a pain, the rug collected dirt so needed vacuuming, and it was heavy so a pain to drag on the trolley. Took too much room in the car.
There are types of double sided carpet tape that are specifically made for easy removal so that you don't damage the floor. We bought a roll from a display company that sets up at the pipe and drape for local shows.
If you're going to use carpet for outdoor shows, just make sure it is water resistant, durable and easy to clean (vaccuum). With outdoor of course there is always the threat of rain and a soggy ground, I wouldnt want to have to load in a soaked carpet into our van, on top of our tables and stuff.