In short, its a scripture on love making and sexual practices to please each other.....
Sex is a very important part of marriage and I feel it is one of the reasons many marriages break up...hence if one knew how to please their partner, it would lead to an environment of a "happier" marriage...
However marriage is more complicated that that and several factors go into what makes a happy/healthy marriage...
My personal opinion is that humans are not meant to be monogamous.....marriage is an element of living in society and many a times is more a compromise than true love....