While the most important lineage was the paternal one, it was still incredibly important to allow for structures and networks which went beyond this group.

A marriage was important, not only by symbolically joining two families, but a as very public declaration of amity between two groups. Your daughter might provide a friendly voice in her husbands court, or conversely a mediator between father and son-in-law.

These are very broad benefits to a father who might marry out non-heir daughters.