I have only seen one article on the benefits of smoking reduction. It took bupropion to reduce me from 2-1/2 packs to 1 pack a day. It took the addition of all the pieces of gum that my digestive track can handle (after they came out with a flavor that I find palatable) to reduce that to 1/2 pack. It took adding the e-cigarette to get rid of those last 10 cigarettes.
The Tobacco Control Crowd get all bent out of shape about "dual use" but it could very well be that "dual use" is an effective tool on the way to smoking abstinence.
I don't think my experience is unique. I think a lot of folks reduce the number they smoke on their way down to zero. My husband did, too.
One thing that is ignored is the dose-response relationship. There is one group of "experts" who claim that any cigarettes whatsoever are a major threat to health. In their book, one cigarette per day does just as much damage as five packs a day. Judge Judy says, "If it doesn't make sense, it isn't true."
If "the dose makes the poison," then higher doses of tar, CO, particles, and toxins would have to be more harmful than smaller doses.