Yes, it instills good manners. My family always thanks me for dinner for example when I cook for them. It makes me feel appreciated which in turn makes me more apt to continue to cook for them in the future :). I think saying "thank you" and "please" are simple ways to show respect and make people feel validated for their contributions. Even when we do what is required of us anyway; it's nice to hear an expression of appreciation. I regularly ask my boys to do things and say please - they do them without argument usually. I also say thank you when they complete tasks - which may be a good part of the reason I don't get a lot of arguments.