I was in the Army and can attest to the hands out of pockets policy. The way it was explained to me was that it just looks unprofessional, and that much military stuff is based off standard and bearing. Certain haircuts, uniform being neat, minimal make up, hands out of pockets, all that is to at least make a soldier (or sailor!) seem like they know what they're doing and that they're the best.

Out now though, got my hands all up in them pockets and making up for lost time. My handsies just feel so comfy in their homes.