I am trying to understand the concept of "married segments" in airline network operations. Apart from being a "back door" devaluation of redeeming award mileage, are there other reasons to employ such a device? I have read flyers commenting on its use with paid fare tickets. Insure same cabin passage for an international traveler transiting to domestic?

Anecdotally, the phenomena seems most common among airlines that have made reducing their FF program's worth a high priority.