ok.. first off.. THC is only located in the resin glands on the plant.. and its actually only in the little head of the gland... THC is not a free moving substance within the plant... the only places THC is on the plant are where you see resin glands a.k.a trichromes... if THC was free moving why would we hang them period? why wouldnt we just smoke stems and all? so thats why the THC in the stem thing is a myth... THC is ONLY located where you see resin glands... the idea of hanging them upside down is for convience.. you can fit a lot more buds in a room if you hang them on lines than if you had a big mesh screen that you laid them on to dry...
secondly its best to let your buds dry slow... if the exterior of the bud drys to fast you could think its ready to cure, but it could still have a TON of moisture in the stem and center of the bud.. if you go to cure it and its like that its a perfect setup for mold and mildew... you want to let the buds dry slowly over several days to make sure the moisture in the middle is sufficiently leached out before curing... most mold/bacteria cant grow in conditions with less than 15% moisture... so its important to make sure that the buds evenly dry to avoid the situation where mold can grow.. which means a slow even dry works best..
i personally trim the branches from the main stem and trim the buds while on the branch, then i hang them.. i leave an inch or so between branches for air movement.. i keep them in a dark area with a fan going for circulation and dont allow humidity to get over 60%.. i personally like a slighty more humid drying room so the buds dry slower, again to avoid mold later down the road.. i just make sure the room has plenty of air exchange and circulation so the buds dont mold on the stems... it usually take 5 to 7 days to get all the buds dried enough to cure.. then its another 5 to 7 days of curing in mason jars... which get burped 3 to 4 times a day...
like i said earlier, hanging them is purely convience... its quick and space efficient.. you can also use a big mesh screen, like from a picture window, as a drying rack.. just prop the screen up with some chairs or whatever... and waa laa.. giant drying screen... still need good air movement in the room... but works just as well as hanging them if you so choose...