For me, there are 3 reasons to protect the chassis:

(1) teflon cloth or mylar tape has less resistance when scraping the ground. This results in faster lap times

(2) when you drag your chassis on pavement, you wear it down. Over time, this will make it substantially weaker and prone to flex, crack, and fail

(3) it looks better when your friends and fellow racers pick it up and check it out.