using your ranged attacks and your splash damage you can deal a lot of damage to foes you don't even focus. This effect annoys a lot of people, it also gives a kind of crowd control called crowed damage. The splash also hits the target, which duplicates the damage fast and easy, which makes it easy to deal a lot of damage really fast. When using surge you are able to attack faster and deal a huge chunk of damage
, while using heal you can get damage going for longer time than usually. And also, your ranged attacks make sure that you can attack before your enemies can. The crit Quintessences make sure, that you will crit, when it's working together with Ashe's passive effect. When you hit critical damage, it will also be splashed to nearby foes.