It also contributes to the high.

When I was smoking I found that they enhanced the effects of other drugs. Since it's a stimulant it keeps you from getting sleepy when you're drinking or smoking weed. With coffee I found it smoothed out the jitters and let me work a lot longer without needing food.

That being said, the constant stink on my clothes and the huge price of cigarettes got me to switch to vaping, and I'm reducing the nicotine concentration to help me kick it entirely.