Please excuse me if I'm misunderstanding something as I'm not very familiar with Greek culture and legends of the time, but from warty goblin (another infrequent poster on this thread), I was under the impression that in Ancient times, great emphasis was put on the earning of
kleos, that is the earning of glory through great deeds.
Since spoils of war is one of the direct measures of your great deeds, earning stuff from raiding or killing important enemy officers would imply great military valour. In the Illiad, when King Agamemnon takes Briseis away from Achilles, he's directly taking away Achilles' kleos, resulting in Achilles' first temper tantrum.