From what my nephew told me I believe it to be a crisis point. He said the pain that comes from self harm takes the mind off the deep emotional turmoil. So it might prevent suicide in some people. This might not be the case for everyone that harms but it it what I gathered from talking to him.
The initial wound pinches yes, but if the blade is sharp enough it cuts through quite easily, like a scalpel would not hurt as much as a knife. I find the release of blood to be rather interesting and I find my concentration goes up afterwards, perhaps as a result of a traumatic event.
I have not experienced a life threatening cut however, that may be a lot different, but it would be interesting to test if there was a way to do it safely. Chop an arm off with an axe and have a surgical team sew it back on right away or something.
I read that death from loss of blood is painless, aside from the wound damage of course.
Hurting myself doesn't affect me emotionally, and I don't hurt myself when I am upset either, which also invalidates the above comments I suppose.
I didn't realise that makes a person act in precise ways I thought maybe the imbalance might change a persons mood a little bit , but not necessarily trigger a person to that extant .
I think I read that somewhere but that's not to say that I think that everyone who self harms has a chemical imbalance. I am sure there are many reasons why people do it.