- cigs would temporary sharpen senses but would cause long term addiction with all conquensenses
- alcohol could supress hunger and thirst for a while, but when consumed too much would work the same way as in reality
- Legacy ID
In post-apocalyptic world full of zombies and enemies while surviving, you would be happy for any kind of happyness.
Especially when you were a smoker before, you would search for cigaretes and most people for alcohol bewerages and those would become matter of trade.
Also this behaviour has another dimension too - it adds immersion to game - its one of those little things that makes game more interesting and gives players human behaviour. (and opens new opportunities for gaming situations - for example - detected by smoking, throwed cigarette could possibly get wood (building, anything) into fire, you could use gas and lighter to burn something on purpose, torture captured player with lighted - make him wounds or "tattoos"......)
Don't think anyone in a post-apocalyptic world cares about the consequences of a few smokes here and there... on the other side, smoking a cigarette can give a temporary effect. The same could be achieved by drinking any kind of beverage that contains alcohol.