I leave mine in the car and mostly use it for padding and protection (hot or cold cart) not germs (those things are everywhere anyway) and to prevent my baby's leg from getting those marks from the cart. But there are some carts that are just utterly disgusting, I wouldn't even put the cart cover over the cart let alone the baby. Have you seen those carts? The dirt and oil is caked on or pasted! It feels grimmy and sticky. When I know I have to go to that store I leave the baby at home.