Some people use paper bags to help speed up the drying process. It's beneficial to those living in a more humid climate because the thick brown paper will easily absorb moisture. Those who do it in fall or winter and live where the air is drier are basically wasting time and run the risk of over-drying their product, IMO. For example, a "winter" grow that is harvested in April-July, but grown in a humid area like the south or western US may find it beneficial to use the paper bag because of the excess humidity in the air, thus helping to dry the harvest a bit quicker, yet still evenly. People in the north or east should have no problem hang-drying their harvest if it is done in September-January because the air is much drier in winter.