Basically like the name states, having emp weapons do increased damage to shields.
Most emp effects get completely blocked by shields, and some units that rely on these do overall less damage.
List of units it would be effected are admittedly mostly cybran.
SACU stun upgrade
Medusa have rather low dps for a t1 arty and rely on the stun. Makes the emp more relevant when there are mobile shields.
Shimmer (Aeon bomber) has low damage. Not very relevant change to it but its something.
Fire Beetles would have some more uses.
Loyalist charging in with their ability may have a function even if bricks are out?
SACU stun gets blocked by mobile shields and is a rather expensive upgrade. Could make it have a stronger function against shielded targets.
If other units need to do more damage against shields, they could perhaps have an emp effect added as another option for balancing units dps output.