Shuriken can be used to break the glass on Corpus missions, activating a lockdown. Trapped enemies inside the room are slowly damaged or even killed if they are weak enough.
Shuriken will often try to seek enemies that you've run past, making it miss both the enemy you ran past and the target you were trying to hit.
Blade Storm can be activated while zooming in with a ranged weapon. This can be used to more precisely pick targets.
You are invincible while using Blade Storm. This can be used to give time to regenerate your shields.
Blade Storm can be used to pick up items that are very far away or in dangerous situations (an item surrounded by 5 enemies for example). This generally requires a sentinel's Vacuum skill for maximum effectiveness. Simply target an enemy near something you want to pick up and activate the ability. Since you return to your starting point you will return to your "safe spot" but will have picked up health orbs, energy orbs, and even mods.
Ash is a poor choice in Defense missions unless using a heavy hitting or heavy crit chance melee weapon, and even then consider using Ash for missions other than defense. He lacks a quick, high damage AoE ability that can decimate groups nearly instantaneously such as Volt's Discharge, Rhino's Stomp, or Excalibur's Radial Javelin. Ash's only AoE, Blade Storm, is potentially time consuming and the cryopod/artifact could be destroyed before Blade Storm kills everyone in the area.
However, using Smoke Screen and then attacking with a melee weapon(preferably one that can strike multiple targets) can clear out a group faster than Blade Storm, if base damage is high enough, due to the bonus stealth damage.
In Update 13.5, Ash's Blade Storm was buffed to increase its viability in AoE crowd-clearing. Blade Storm now spawns 2 holographic clones of Ash to assist in the execution of Blade Storm and they inflict Blade Storm's full damage. This allows Ash to clear the maximum 18 marked targets 3 times faster, making Blade Storm a viable method of quickly clearing out enemies. Note that other abilities can kill enemies faster than Blade Storm, even with the clones.
Smoke Screen does not prevent damage from Orokin Lasers or AoE damage such as poison clouds and explosions.