(Anti-nicotin lecture)
People smoke (well, keep smoking after they started) Cigars and Cigarettes for the same reason: Nicotin.
Although Cigars MIGHT be a bit better for your lungs, I have no idea why you want to start messing with that awful dangerous super-addictive drug.
Nicotin is a vasoconstrictor and might help you to gain higher blood pressure, which might benefit freediving a bit.
Nicotin also elevates your basal metabolism, which is defenitly detrimental.
Nicotin also changes your brain's pleasure centers in a way which will make you dependend on having Nicotin for them to keep working the way they were supposed to work. Which means that people don't really enjoy Nicotin, they just have problems enjoying stuff without it after they got hooked. Which makes it one of the most stupid and sensless drugs I can think off.
Maybe it's not true to 100% of the smokers, but it's defenitly true for hundreds of millions (if not billions) of people around this world. From what I read, nuerologists and behaviorists agree about the effect. The specifics of what it does is not yet fathomed. It also affects concentration (if you get off it), and it seems that it might help altsheimer (spelling?) patiants to keep their memory a bit better.
One of the facts I've seen in some BBC program regarding addictive drugs (of all kinds), was that Nicotin is statistically the most addictive. Only 6% of the poeple who sign themselves to programs for quiting it actually succeed. A lower success rate than Alchohol, Cocain or Heroin. Ofcourse many stop without programs, and many don't REALY wanna stop since it's a drug you can live with (if you can call that 'living'

), but it's not a very reassuring statistic.
PS: Regarding cigars, you can google the net for some Oral (gum, mouth, throat whatever) cancer pictures, it also exists.