Yes, couples should live together before they get married, so that they know what they are getting themselves into. Plus, we are in a new era where this subject matter is more liberal. I feel that if a couple lives together before they get married, it shows how truly compatible they are, because each person is different in their own space.
Couples should most definitely live together before getting married in order to gain a "preview" of what life would be like with that person, long term. There are often traits and habits (such as cleaning, organizational, and spending habits) that are vital to two people getting along in the long term, and those can only be learned by the other person when being in close proximity to them for a period of time. Two people living together is not something that should be taken lightly, however, it is the only way to truly understand a partner and work out any issues one may have with their partner, before entering a legal bond.
Second, two people make a new years resolution to lose weight. The first says "I am going to exercise" but takes few steps to keep himself accountable. The second says the same thing but then signs a paper and has friends sign it and make sure he goes to the gym regularly. Which person seems more committed to keeping his word? The same can be said of marriage.
While there is nothing morally wrong with living together as a couple before marriage, it usually ends up badly for the people involved, such as family and friends of the couple. Men who live with their girlfriends may be more likely to prolong marriage and/or be unfaithful, because they do not feel "tied" to the relationship. Either way, it is a personal choice.
Okay, so the couple moves in together before marriage. They enjoy the new feeling of sharing space, seeing each other daily, cooking together, laundry, etc. Then one day (maybe) they finally decide to get married. The wedding and honey moon is so beautiful and exciting. After the honeymoon, the couple returns home to what? The same thing they had before they got married. What's new? What's changed? What is it that makes you so happy to say that you're married? Nothing at all. Why would a couple want to forfeit the beauty of a new marriage just so they can experience a "common law" marriage as just boyfriend and girlfriend?
Not to mention, suppose they break up before getting married. Now a new relationship starts and eventually he or she decides to live with the person to "try it out" before marriage. So they move in with boyfriend/girlfriend #2. It doesn't work out. Then eventually they move to #3. Live together to "try it out". Why be a serial cohabitator? Just wait until marriage and leave it at that.
I think people should wait until marriage before they decide living together is the best choice. One should not enter into cohabitation unless you are sure that is the person you want to spend your life with. Marriage is the joining of two lives into one, and so is living with one another. If you move in prior to marriage you take away the major significance of marriage, and therefore should wait and let marriage be the initial joining of your two lives.