From my perspective what makes it worth it is that DEF treats the majority of NOx chemically rather than mechanically by punting to under hood emissions components, thereby reducing engine soot.
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Not sure what punting means off the football field. I am a retired Environmental Chemist with 32 years experience. In the place I worked we bought 50% DEF by the tank truck load weekly. It works by decomposing to Ammonia and Carbon Dioxide gas when heated. The Ammonia reacts with a catalyst and with the NOx to form Nitrogen gas and water. End of problem.