Lying is a sign of intelligence. Lying is the act of using your imagination to construct a false reality close enough to the original to be believable, for self gain, it's one of the highest standards of intellect. Sociopaths, and high IQ people both are generally shown to be better liars. Additionally, kids who lie younger tend to be more successful in life. Speaking only truth just makes you a computer, capable of reciting information. Lying shows comprehension and the ability to mix information in different ways. Frankly, a person who could speak only truth would be very handicapped in society and would definitely be suffering from some brain defects. Whether or not you consider those defects a bad thing is subjective but I bet they would also have problems with imagination and maybe critical thinking. There aren't any advantages I can think of. I can always choose to tell the truth, and choose to lie. I can't see any advantage to giving up one of those options. I try to lie as little as possible for several reasons; it takes more mental energy, you have to commit memory if it's an ongoing lie, it makes me feel worse, and the more often you do it the less credible you are (I prefer my lies to be rare and believed). But using it rarely is not the same as never. Even choosing to never lie is not the same as not being able to.