I'm not sure either, but, nicotine does have some thearaputic effects, just as some have mentioned. I was surprised when my Doc said I should drink a cup or five of coffee throughout the day. It is a country Doc's remedy for Attention Deficit Disorder where the attention is going in to many places. I think it is just PTSD or anxiety relieving at a low level.
Anyway, I think about what I am going to do, as far as vaping, when I get to 0mg nic. I think I will still sit on the porch and vape. Probably worthwhile to do.