For me it depends on if you have bentgrass or poa annua greens. Bentgrass survives the winter much better than poa annua. Clubs that do have mostly poa greens cover them in the winter to protect against winter damage caused by rapid exposure to cold temperatures, prolonged exposure to cold temperatures, desiccation, freeze-thaw cycles, extended snow cover, ice encasement, and disease. In my opinion, covers can be effective tools for protecting greens against freezing temperatures, ice encasement, and desiccation injury. Not using the proper cover can lead to toxic gas build up and/or anoxic conditions. Under anoxic conditions (lack of oxygen), the plant will run out of energy and eventually die. Therefore, covers can be extremely effective tools if the right materials are used (Crystal Downs).