Well, if you start with a shot against an incapped enemy, that's a capped hit chance, then you've got two more tosses of the RNG dice before you get a chance for a stun, making all your subsequent attacks very likely to hit.
It's fantastic for taking down high-health organics, like bosses on DOMINATING. You get all buffed up and can get 12+ attacks a round, you can land devastating 12th hits with pneumatic + combo going off. If you've got a target-rich environment (and maybe Fleet Footed edit: I meant Fancy Footwork. Words are hard.), you can use your weak shots on the squishy trash and your heavy shots on armored foes, making high enemy DT pretty useless. It shines in fights against Burrowers, for example, since you've got weak nothing enemies to soak up your normal hits, and then the Burrower Warriors to take your heavy shots (and put stuns on the normal Burrowers if they're nearby, too, so you can deal with them next turn).
So, yeah, you don't need it against leather armor clad Lurkers or such, but if you can plan out your turn and have high mobility, it allows you to really take advantage of the cadence of battle to clear out groups quickly. Almost no reason not to take it if you've got the Dexterity.
