First marriages don't always have creation of children as a important part of the marriage. There are so many reasons for this I will not waste time here explaining unless someone really wants to know.
Second marriage is the bond of physical and mental bodies together for hopefully eternity
Third the savior taught us that to love another as we love ourselves is important, in doing this we fail to see the short comings of another and also ignore some of those in our selves. I say some because some short comings we have need to be addressed like maybe tithing, helping others, callings in the church which we feel inadequate in
Fourth marriage is a commitment to something greater than ourselves, when we marry we say we will honor our spouse in sickness and health and in wealth or poverty and to be one with them
Fifth marriage today is becoming a joke in the fact we see so many marriages end in divorce because it is so easy to get one. Does this mean all divorces have no merit no it just means there is a lot of them for stupid reasons and they could have been saved if the partners had wanted to work to save them
Sixth it is a known fact we live longer if we are in a loving relationship with another and not living alone. think of it as your personal fountain of youth because you have to get up each day and see what you spouse has figured out you need to do today.
Seventh wasn't it a commandment to marry and replenish the earth, but does it say anywhere if you can't have children to have sex and not marry? Sorry but marriage is a bonding of bodies literally as well as mentally and there is no reason to believe because children are not part of it that it is any the less a scared commandment we should follow.
last and most important it teaches of tolerance, love , compassion and humility