3/20/20's

hey i have been playing lod for a few days now and im just wondering why are 3/20/20 worth so much. i do nt really find 3 to max dmg, and 20 to life bad but 20 to ar sucks kinda it wont even add 1% to ur h9it rating in hell and i dont think it will in normal even....the only way i find them any good is if the persaon has like 5 or more cuz then they aint bad, but 1 or 2 suck. well i dunno if i ever get one ill gladly trade it but like someone please tell me why there so good? i personally think they arent