League of Legends (LoL) Question: Hello everyone I`ve seen the Glacial Augment and I`ve been wondering if it

No, like the others have explained it is beyond useless.

For AD Carry Ashe take a precision keystone like (probably best to go Fleet Footwork or Lethal Tempo).

For support Ashe pick Dark Harvest (I'm not kidding).

About as viable as stacking 6 Tear of the Goddess on Amumu.

Slows don't stack. Glacial augment on a ranged champion slows people by 40% at most. If you build crits on Ashe, your autoattacks with your passive slow by 60% instead.

It's terrible on Ashe. The way multiple slows work in this game is only the highest of the slows you have is applied and the rest are ignored. Frost Shot already slows the target by a decent amount and it equals Glacial Augment when you crit. You'd be better off with a keystone that improves your damage output like Lethal Tempo since you have a built-in slow from your passive.

If you're seeing Glacial Augment used on mages, it's to take advantage of the really strong slow field from active items. Everfrost and Twin Shadows both gain extra slow fields from the keystone which adds a ton of CC to a mage's kit. The slow-on-autoattack is only prioritized on a few champions ( Sion, Tahm Kench); most others are using it for this active item effect.