I built my own skid plate and A arm guards. The reason you need them was stated above. Also I like to let my machine ride as low as possible to keep my center of gravity lower and help with cornering. When you let it ride low then you are going to bounce the belly off of things (ruts, rocks, trees and so on). I have heard people CLAIM that plastic is great but I have personally seen sticks and rocks go through HDPE and I DO NOT trust it as protection. I did 1/8" aluminum and I can jack the whole buggy up on it and it wont dent or bend. Plus its only like 12 lbs total. If your just kicking around the yard then no need for underbelly protection. If you are SERIOUSLY running off road then you need it. Also it protects my axles from sticks and rocks also and the way I made the A arm guards it adds strength to them as well.