Especially amongst Early European groups that practiced exclusive cultural gender roles
It wasn't just the Greeks, pretty much all European and Middle/Central Eastern cultures, up until photographs became widespread and those practices went underground.
In this "Warrior Subculture" the practice of a providing the leader or head warrior of the group with the most feminine subordinate to act as both confidant and "pressure release valve" was fairly typical and not commented on. That subordinate was often described as the Leader's "beautiful son or brother" or "best friend", and was typically also a competent enough person already being trained to replace the leader or become the advisor/confident of the next leader should something happen.
Think of Achilles and Patriclus.
The issue comes from a very, very deep cultural fear that Women are somehow dangerous to Men - that even though it can be unpleasant or culturally unseemly for a man to take a submissive sexual role, a Woman, who is capable of giving life, is also capable of taking the "life" of the male manhood, which, of course, is the whole basis of what makes a Warrior a Warrior.
Laying with a female before battle saps one's manhood and takes away their power into that dark space of life and death.
Laying with the designated submissive releases pressure, and potentially grants that man some of the leader's strength, if the sub is being also groomed for leadership. (Possibly David and Benjamin? That relationship has often been discussed to be a potential dom/sub warrior relationship)
That sort of superstition lingers in a lot of male competitive arenas - especially in sports and military
Even now, a soldier or sailor who "crossdresses" at command events in a sexualized comedic manner is still not unheard of in most Militaries.
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