My hive is from the bottom up: screened bottom board, slatted rack, medium box, medium box, medium box, etc.
I'm in Atlanta and keep my screened bottom board open all winter long. I don't know about other parts of the country, but have read about a lot of beekeepers who do not close up the SBB in winter. The bees keep the cluster warm, not the hive. I imagine if you are somewhere where you need to wrap hives in the winter, you wouldn't use a SBB all year round.
Linda T in Atlanta