M&F has mechanics for marriage and relationships in general. As M&F has family trees and successor ship it is necessary to have mechanics that allows players to formally enter relationships. The mechanics are mostly related to displaying the relationship on relevant character pages and for allowing both players to create characters that are children of those in the relationship. It is possible to form a relationship/marriage that does not allow for children as well.
It has no affect on battle mechanics, but then entering battle is very different in M&F. I am all for formal and recorded marriages in the game. Forcing me to not participate in a battle though I would not endorse. It may well be I am more loyal to my realm then to my relationship, do not attempt to enforce some standard of behavior. If I do not wish to fight against my spouse and/or their realm I have mechanics to do so, it is called not showing up to the battleground.
