to my understanding by placing in mason jars for curing allows the remaining moisture within the bud to even out, and allowing excess moisture to evaporate. this creates a "sweating" effect and this is why it is nessesary to open the jar for a few mins each day - to allow the excess moisture to leave.
Over several days, this leads to evenly dry, chlorophyl (sp??) free weed
this is just from reading and my own basic scientific knowledge, so correct me if im wrong...