I think the practical manifestation of duality is less about physiological balance or completeness. So you are correct in that assertion. Rather it is in fact about psychological comfort and ease of communication. What that means in its real world manifestation is that you are able to freely exchange ideas and trouble shoot problems without psychological or relationship repercussions.

Basically, interacting with a dual will allow you to troubleshoot your personal problems without fear or having to jump through any hoops. When it comes to self improvement I.E. behavioral/intellectual/interpersonal development duality would likely be more beneficial than other inter-type relations.