PvE mobs are very easily distracted by clones. Each time one of your clones is being targeted is a time someone in your team is not being chased after. Now add the 'cripple on illusions death' trait and the AoE slow has made the mobs chasing your team even less of a threat. Couple it with the 'clone on dodge' trait and the 'vigor on crit' minor and there is a blanket of safety you are casting over your team over the dubious DPS increase of a shatter.
In a game without tanks and healers we need to shoulder part of the burden and can't go deep into the role of 'I'm DPS only, you deal with it'. I would advise on not being lured by the 'max DPS0rxs!' crowd as we have no DPS meters and not even enrage timers, outliving a boss is generally better than trying to squeeze a few hundred more damage.
This makes some good points, but remember of course that with Deceptive Evasion + Mirror Images or a Scepter, you can create so many clones/phantasms that you can throw up 3 distracts, wait until the mob almost reaches them, shatter, and immediately make 3 more.
Of course, it all depends on your play style, what you're doing and who you're doing it with. I run with high DPS warriors who tend to keep all the aggro (and won't benefit from cripple - I wish we had Chill!), and we wait until they're low then use Temporal Curtain/Into The Void to drag a mob off them, or use the same skill to save a downed player who's still being targeted. Magic Bullet is a great player-saver as well.
Also remember the value of Blink + 3 illusion Distortion as a fantastic res combo. Warrior Endure Pain is great for it too, but on a much longer cooldown than our Distortion and they're more likely to need theirs for melee survival.
I really do wish that Diversion was more useful.
An unsaid point about not shattering vs shattering would be of course if you have up 3 staff clones with Illusionary Elasticity, you can give your team mates like 7-8 stacks of might occasionally, a lot of Fury, plus a lot of conditions on the enemy.