The whole point of this build is to kite fleeing enemies to death. Because of how much slow and stun ashe has, this is the perfect thing to do for her. She is especially good in teamfights as she can help her teammates take down fleeing enemies who haven't died yet. She is also good in teamfights because of clarity and the mastery which allows all nearby allies to get mana.

Ashe's runes allow her increase attack speed, critical chance, and cooldown reduction. so she can spam her volley to farm minion waves and attack distant enemies.

Ashe's offense masteries allow her even more increased crit chance and attack speed, the bonus ap mastery was to access the attack speed mastery. Her utility masteries are vital as they can really help keep you in team fights.

the point of the skill sequence is to farm minions unless you are playing on Twisted Treelines and you wish to go for a gank. But the main focus of maxing out volley is so that you can farm minions early and hopefully have an advantage over the enemy team.

Ghost is an effective summoner spell when kiting enemies as it will increase your chances of hitting your enemies more and keeping them slowed for longer. Clarity is effective in team fights as it will grand nearby allies with mana which can help when any of your teammates are about to go OOM (out of mana).

If your going to play Ashe my way, play her as the best kiter you can be. Because of you don't, then there is no point of using this build. Hope you guys enjoy playing Ashe. :)