i think it does, chemically; that's why we have tears, i believe. I've seen some research papers on that before. could you maybe look it up KazzaX?

for me crying in session is definitely a pressure relief.
If I can't cry, the tension builds up unbearably (sadness, grief, fear, you name it).
If I can cry, it's better.
Often the tears just roll out; just a couple of times I have boohooed, and although at the moment it feels just miserable, it gives a voice to the emotion, and I do think it's better than the internal pressure buildup (does this make sense I hope?)

one thing about crying for me - I never look at T at those times - if I did, no tears would come out I'm sure.