I used to hold my hits in for as long as reasonably possible to but then I saw somewhere that it only takes a couple seconds for your lungs to absorb all the THC in the hit. I recently started smoking my weed like tobacco, holding it in just slightly longer than a cigarette and I didnt notice any decrease in the high, just less discomfort and coughing. Another thing to consider, if you smoke alone the longer you hold your hits in the slower you smoke and the longer your weed just burns.