I would venture a guess that generally ( I do not hold this perception, of course) that smoking should be done socially, and that if you do it alone, you're more of a "heavy drug user" than just a typical social drug user. Sort of like the difference between drinking at a party, and drinking by yourself in your room. This is merely guessing, though. Kind of an interesting question. I, personally, enjoy smoking by myself a lot more, actually. It's nice to just chill by yourself, play video games, listen to music, take a shower, whatever.