Scraping the plastic underside cover

every once in a while, my milly scrapes the underside plastic cover thing between and a little forward of the front wheels(i explain it this way because i have no idea what its called). is this a bad thing and could i get it replaced easily later if its damaged enough that i have to take it off?

Mine got pulled off when trying to leave a friends house where i had to park in his yard. The only thing I have noticed was that it is louder when outside the car. Some cars these things actually have a cooling function but I have not noticed a difference yet.