From my indirect experience with a couples match, (one of whom successfully matched into a competitive field), you do not automatically interview together unless you explicitly try to request it. (the only exception I seem to recall for them was MCW).
The reason couples do not interview together automatically is mainly because different departments do not communicate well, so you must request them to coordinate interview times (assuming both of you receive interviews!).
The only exception I suppose is if you are both matching for the same field (ie medicine), in which they would pay attention to both your needs.
One advantage I've heard of the couples match is that if a program director really likes you, they may pull weight on another department to let your spouse in. For example, you are an outstanding medicine candidate, and your husband is trying to enter surgery...the medicine department may talk to surgery to help your husband's chances.