Given the lying to children question, I think I need to reword my answer from earlier: I never lie for personal gain. Continuing the Santa myth or making up fantasy worlds (love the battle station moon) is just storytelling, it’s good indulge developing minds in fantastic ideas.
There’s no need to lie in social interactions, just as there’s no need to go into every detail about whatever ails you. I’d rather someone gave an honest answer rather than the standard “very well, You?”, “not bad” or “mustn’t grumble”. Those answers just feel like shorthand for “I’m not really interested in you or what you have to say”.
The key is knowing when to stop with the detail, by opening yourself up just little bit you tend to find that it often develops into a proper conversation between two people rather than a social nicety between strangers.
And another question. Do any of the non liars ever feel a bit of a mug when you see other people gain through their lies?