Somebody else just asked this question...so in this rare case...I am going to copy and paste my answer. :-)
I'm probably in the minority here--but I'd say it's good for couple not to live together before marriage. Living together presents a whole bunch of challenges.
People who are married (I think!) are more likely to stay together and make it work then people who are dating and just "trying it out." Commitment is a key foundational element for any relationship to be truly successful. Living together to "see if it works" creates a mindset from the very start that says, "If I don't like this, I'm out." There will be many times when you are highly annoyed and even don't like your significant other--especially when married. But conflict has a positive purpose if handled in a way that makes each other better and breeds intimacy, bringing you even closer if you can work through it.
Living together before marriage, I think, sets the couple up to fail in many areas. They may bail out when the going gets rough, as I mentioned above. Or, they may think "this is what it will be like to be married to this person" and then be in for a surprise when they get married because even living with somebody doesn't show you what its like to be married to somebody. The act of being married changes something in the relationship.
Then of course there are all the details of "if it doesn't work out" its much harder to deal with a break up if you are living with the person! Some people who should break up don't because its too inconvenient or difficult because you are now living with the person.
These are some of the reasons for my answer! Good question.