This has to be a bouncy.
Body language can tell you if they have a head ache, acid indigestion, a sore foot or hip. Use full at times, lets you know if a cop is about to pull his gun on someone or someone is lieing. Great tool for a manager or a parent to know when a child is fibbing.
Far as I know body language does not show if you have pets, what your religion is or who you voted for. However we did take a quickie course in body language one year for us senior workers to help understand the Temps that spoke limited English.
A small mistake on managers part, we began to watch the interaction of the high up together and found out who liked who and placed bets on who was the next manager out the door.