Because smoking is a habit cuts across hierarchies, you can meet a broader spectrum of people than just randomly talk to people at a networking event.
Also smoking time is discreet, so your convo have a natural end without awkwardness.
What is also nice is that you can meet people - by just asking for a light. Most smokers are extremely friendly to other smokers and if two people stands outside a building smoking, it is natural for them to talk. It is the new Freemasons.
I've sometimes wonder why tobacco companies doesn't embrace this with a slogan such as: "Smoking turns strangers into friends".
(I don't smoke myself, but I've ended up in more than one conversation I wouldn't have otherwise had, because I was with a friend who smoked, who approached a stranger in that manner.)