Do you really need it?
Yes! Yes! Our first pool was an easy set pool from Walmart and did not come with the ground cover. We told that if we were setting it on level grass that we really did not need it. Wrong! The bottom of our pool was covered in mud. Not just mud but smelly mud. You see grass dies when it is covered all summer by a pool holding over 5,000 gallons of water. When grass dies you are left with dirt. When you drain 5,000 gallons of water near dirt, you get mud. We rented a power washer but ended up with more mud.
Solution
From the summer on, we use a ground cover. We throw it out and the end of each season and purchase a new one. For about $30 each year, we put down a fresh ground cloth. We no longer have the smelly mud caked on to our pool making our ground smell during the winter.