This glyph is very useful for PvE Elemental Shamans. The loss of the knockback makes it viable for AoE trash fights. At the same time, the loss of the knockback removes much of the PvP usage of the ability.
Patch changes
Patch 5.0.4 (28 August 2012): Changed from Increases the mana you receive from your Thunderstorm spell by 2%, but it no longer knocks enemies back or reduces their movement speed.