Although we grow up with our parents chanting the lines that honesty and truth is the best policy yet we are destined to contradict it as we grow wise.

Even today before leaving for work I asked my 6 year old daughter to be true, honest and humble.
So what happens as we grow, are these feeds baseless which we give to our children, when we as adults are aware that we need not speak the truth at office, to friends, while socializing etc. So why we are chanting this rhyme to our kids. The answer is that we want to imbibe moral values in our kids and let them decide later how to use this based on the circumstances.
Ask me personally there is no harm in it, I can say a lie to make people happy, to bring a smile on their face. People don’t like to share the truth with others unless required and the other person is not an acquaintance . You may praise the dress a distant relative of yours is wearing in a meet up, you just would not like to turn her head up on heels by saying it sucks.
This is noting strange but being smart, you create a space of respect for others, yourself and avoid conflicts.