The road hazard warranty is like insurance, Cesar. If you pick up a nail or hit a curb and the tire is damaged beyond repair, you'll get a replacement tire coverage cost prorated based on the tire ware. It's really up to you whether or not you want it. If you drive on nice pave roads that don't have alot of debris and you never hit any curbs, you may not need it. If you drive where potholes magically appear after every rainstorm, maybe you do need it. It's a personal choice thing.

Charges are usually based on tire size (or actually cost). The more expensive the tire, the more expensive the warranty.