If Shatter buffs allies for 10% of total armor, but Taric still loses armor on cast, then using the ability offensively would hurt Taric's ALLIES as well as Taric himself.
For those that haven't seen or heard, Shatter is on PBE with the following changes:
Shatter ( W ) now grants 10% of Taric's Armor to allies instead of flat 10/15/20/25/30
Shatter ( W ) now also deals damage equal to .3 of Taric's armor.
But, on top of the reduced aura effectiveness, Taric still loses armor when he activates Shatter. So, since Taric's aura buff is percent based, reducing Taric's armor also reduces his aura's ability to protect his allies. So Taric has to reduce his ally's armor buff to use Shatter offensively, making his allies more vulnerable to damage when he engages.
The other side of the coin is that Shatter will now deal more damage since it scales with both armor AND AP now.
So not sure how I feel about the tweak. On the one hand it reduces his aura's defensive power pretty noticeably and I hate that, but it's offensive power has gotten a buff so Taric's initiates and engages will potentially be stronger now, but also riskier since his aura is weaker.
I guess the "adding more risk to gameplay" trend continues on. We'll see what the final numbers are, but personally I'd like the percentage on Shatters aura to be at least 15% since Taric, as a support, can't really afford to build 300 total armor in an average match, or to have the aura ignore the reduction on Taric's self armor so he isn't exposing his allies to harm.