Would have to also include using herb to alleviate what an "uncle" of mine jokingly calls "G.S.S." (Ghetto Stress Syndrome), or any kind of stress for that matter. This is probably one of the more problematic uses of ganja i.m.o., as there are times when alleviating stress can give you an excuse not to deal with the underlying causes of the stress. But definitely there have been times when herb has helped me calm down from stress and anger - like from having a bad day at work, or having an all-out blazing row with a girlfriend. I can remember being absolutely livid with fury during one argument, going out on the roof and burning a spliff, and coming back being able to have a quiet, reasonable, loving conversation with the wombman in question. Then again, it wasn't like that spliff stopped our arguments - blazing rows were a part of the nature of our relationship, it seemed like.
So the benefit here would be a calming effect, helping you to rise above your angry state and look down on it more "objectively": the cost would be potentially relying too much on this calming effect when (a) sometimes there are good reasons to be stressed and angry and you need to deal with those before trying to "calm down", and (b) you need to find your own ways of calming yourself down without depending on any substance.
I'm sure there's more benefits/costs I could think of but the above is quite an important one I think, so definitely wanted to mention that. That'll do as far as a general summary of em I think.