Well there are something like 2 million people that speak it worldwide, but mainly its useful for learning the theory of languages and how they are supposed to be put together with experts doing the designing. Because of this, learning Esperanto is supposed to shave at least a year off the learning time for other languages, especially European ones.
Its also supposed to be way easier to learn than natural languages; small vocabulary, phonetic alphabet, etc.
And, as much as I hate to say it, Liberals are sometimes right; learning a second language gives you a broader, more international perspective that is not as subjective and dependent on one nation.
And, personally, I kind of like the idea of a language designed to help prevent wars and conflicts due to misunderstandings. Maybe these 2 million speakers are Voluntarists and they don’t even know it yet!
And, I have already seen first hand, that Esperanto is an awesome conversation starter with people. It sounds familiar to people, but they can’t quite place it.