Why do people date? why do people cheat?
why do people break up?
serious answer

People date because they think they find interest in each other and they want to express it by hanging around each other more and going places together, maybe even alone.

People cheat because they either saw interest in the person they were originally with and weren't interested anymore, then didn't want to tell them, or they used them completely. (meaning they never liked them but pretended to) 

And people break up because one didn't think they wanted it anymore, they fought and thought it wasn't the best situation for them, or they aren't emotionally invested. Or, someone around them who loves them unconditionally didn't like the fact that they were dating to begin with.

I hope those are serious enough answers and that they help! :)

Keeps you from getting lung cancer from smoking

Because without physical activity, the body has extra "energy" if you will, and so when it is time for bed you are not tired, so you end up staying up all night. also there is probably an effect on your internal clock, which messes with your melatonin production which goes hand in hand with your sleep cycle