Hello Waldemar, My hives are in 4 deep boxes now but will be reduced to 3 deeps for winter. I previously overwintered my hives in 2 deeps, a practise carried over from my commercial experience. However, I don't migrate and have found that the bees overwinter better in 3 rather than 2, similar to the studies noted in the Hive and Honeybee in the chapters on overwintering. Also the extra feed insures an adequate food supply during late winter through early summer. Often the weather here is very unsettled and a strong hive can easily starve or destroy brood during the bad spells. A slower developing hive will often have extra frames of honey which can be easily used for splits, etc. Pollen is often preserved under the capped honey and can be more important than the honey itself. Overall I probably could extract more, but most who run only 2 deeps here end up feeding syrup at a very critical time around the first of June. I haven't noticed any decrease in my hives production. I think larger colonies are produced earlier which produce more honey and offset the additional stores left behind. Also the bees don't have to be disturbed during our cold, windy springs. Also, I have been infected with a bad almost incurable disease from my commercial beekeeping days. It seems I am always adding hives or equipment or expanding. Anyway my wife has been giving me some nasty looks lately while trying to get out of her car and around my bee equipment in the garage. An extra box on the hives helps in that situation. :>) Dennis