I got started in the military. Flat out, smokers got more breaks and some considerations that others didn't, and so yeah. Light 'em up! And I was in during the late 80's when smoking was basically everywhere.
Smoked for many years, and was on strong cigarettes. Very hard to quit, and I tried a few times.
The impact was noticable later in life, I was easily winded and had some minor league emphysema beginning. Not good.
I had by chance mostly tried a vape. And it sort of worked, but did not deliver the levels I needed. Nicotine salt does. I did one vape on that formulation, and that was it. No more smokes.
Some years later, my recovery has been dramatic! Some basic damage is not going to heal, but most everything else has and I feel great! Can do what I should be doing too. And the benefits continue to accrue.
Coughed up bits of tar for a long time. On another whim, I did inversion, and gakked out a ton of the stuff. Recommended, if you've got clogged up lungs. Just make sure you've got a spotter and someone to assist you in the process. I needed that due to the exertion.
Moving on...
Vapes are seriously good harm reduction, assuming someone is using gear that isn't damaging somehow. There is a lot of crap out there. Sadly, rather than regulate it all and maximize the benefit, the pressure to get rid of vaping altogether is winning out here in the US.
Too bad JUUL was run so badly. Their core mission is a good one, and tons of people are going to benefit very significantly.
Nicotine itself isn't that big of a deal. It's a stimulant and is addictive like similar compounds are. What really maxxes out it's addictive nature is the inhalation delivery method. Taking it orally, for example, isn't quite the same thing, unless the method is intended to pass through the skin, like chew does.
Nicotine is not cancerous.
The real danger in smoking is tar & particulates damaging the lungs, and cancer caused by the tons of byproducts of the combustion chemistry. The nicotine comes along for the ride and again, by itself isn't such a big deal.