working with people who had various mental health problems, I observed that smoking did help when someone was having a bit of a panic, not because of the nicotine but because it forced steady controlled breathing, and because it was a fixed length of time-out before going back to a situation or task. A non-smoker, you'd take them out and chat and mooch around and maybe get a drink, it'd take half an hour or more, or they'd keep saying "I can go back in now" (three steps towards door, panic attack starts again) "no I can't" whereas a smoker would light a cigarette and not consider going back in until it was finished, takes pretty much exactly five minutes of steady breathing. Not that I'm advocating smoking of course. But that's my theory as to why it helps particularly nervous people to calm down.