When is it good to Sand/ Media blast your car?

would you do the enitre car with wire brush? Jw because I wanna take the under coating off as well

if your working on the underside (floors and subframe) a wire wheel and some elbow grease will work, if you mean wire wheel painted surfaces.... NO!! don't do that, sand it down if theres more then one layer of paint, but don't sand it until you can primer it because you will create a whole 'nother battle with surface rust