My players are a tricky bunch, and I've recently had them using the multifire rules to their advantage. Here's how:
When fighting vessels with high shield Thresholds, they don't use multifire. The reason being that (for example): Their ship shoots five multifire bursts from a Type X phaser at an enemy with shields equal to a Galaxy-Class (Threshold 400). Even if all 5 hit, the combined multifire damage is 400 - not enough to get past the Threshold. So they fire single shots multiple times (incurring the Multiple Action penalty). Again, none of the shots can penetrate the Threshold, but each shot does 200 damage to the shields. So before, they hit with 5 beams and knocked the shields down 33%, now they hit with 3 and knock them down 50%!
Against ships with lower (150-250) Thresholds they'll use multifire because any damage getting past the shields is multiplied by half the number of hits, usually doing more damage than a single shot would (assuming it could get through the shields).
It's often quite hard to rule whether or not they can do this, since they can only manage it against ships in the SRMs, as I keep the stats of my own designs carefully hidden. They're using "Player Knowledge", but it can be difficult to spot exactly when they're up to it.
Does anyone else think players should be able to do this, and if not, how could I guard against it?
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"The more top brass briefings I attend, the more I want to take a phaser to the whole lot of them..."
Captain Matt Hunter, USS Tempest, NCC-81205