One good thing is the ritual. I never thought of it as "brainless" before but that's a great way of putting it. Smoking is relaxing because you turn off your brain and go through the prescribed motions. When you finish the last motion you go back to life. It's not really relaxing in the chemically induced way (in fact smoking increases anxiety), it's more like meditation. You're allowing yourself to take a break from life for a few minutes. In fact, you're really being /given permission/ to take a break by the external mandate of addiction cravings. You can use this time to reflect, strike up a conversation, examine your surroundings, whatever you want.
Another good thing is bonding with smokers. It's a shared activity. The act of smoking serves as either punctuation for a conversation, or the background noise that substitutes conversation. A cigarette can be a prop used for emphasis. Bumming a cigarette is a sort of friendly offering. Most importantly, misery loves company. All smokers know they're addicted. When you smoke with someone else, you're acknowledging each other's weakness and demonstrating acceptance. That's one of the main reasons being a smoker is like being in a big, secret club. It's very romantic.
I haven't smoked in a very long time, and I realize now that it was a really stupid and damaging habit, but I do miss parts of it. I've promised myself that I can take up pipe-smoking as a reward for surviving into elderly age.