He also reduces their attrition, meaning they incur lower damage and so spend less time in port getting repaired.
However I'm not sure if Light Ships stop giving Trade Power boosts when they're in port repairing? I had a feeling they did, based on possibly seeing fluctuating Trade income corresponding to a big fleet getting repairs. And of course that would be logical and most realistic.
But it's possible that once you click the Protect Trade mission, they provide the boost permanently (once they've moved to the right zone at least,) even when docked for automatic repairs.
Anyone know?