Imagine hooking yourself up to a lie detector and then having someone quiz you about all the things in life you weren't sure of. You could do away with almost every doubt you have about yourself. It wouldn't be perfect, obviously, but I mean, it would really put your mind at ease about alot of things.
Instead of second guessing your motivations, you could get the things you aren't sure about settled easily. It would take away so much of the guesswork. It wouldn't be for everyone, and I'm sure that if you went into relationship questions that things would turn bad quickly for most people, but even so.
I just think it's an interesting time we live in, given that psychology and technology could hypothetically be used in such a manner.