These days seem to be times of relativism. There seem to be no real morals, no real sense of commitment. This is also a time where there is a proliferation of couples living together, either before marriage, or in lieu of it. This is a symptom of the non-committal society in which we live. There is, however, no good reason to live together. In act, there is a case against it.
One of the reasons often given to justify living together is to get to know the person before marriage. This is to "test the waters" and look into compatibility on various levels, including sexual. What is interesting is that this method has done little or nothing to improve divorce rates. In fact, they seem to be worse. In the United States, 1 out of 2 marriages end in divorce. If this "getting to know you" strategy was actually valid, this statistic would be a lot lower, but it is not.
One reason is that the relationship is beginning with a non-committed attitude. They couple is going into the relationship to see how it goes, and fully willing to jump out at the first hints of real problems. This behavior is not challenged in the living together phase, and thus is carries over when the couple actually does get married. They have never had the skills developed to handle real problems in a committed fashion.
Another reason living together is not a good idea is that there is sex before, or without, marriage. Keeping religious arguments out of the picture for the time being, is still can be argued that this is not a good idea. Again, what we have here is an example of "putting the cart before the horse". The idea of sexual intimacy is just that,