What are the disadvantages for body language?

advantage

convey emotion into thoughts (swaying hips to demonstrate waking using hand signals to represent other people emotions explain more in detail what your trying to say people might get the gist more that way 

disadvantage

giving possible wrong signals ( showing hand signal that might give the wrong imprssion of what was actually taking place ) not having an organized language you be hard pressed to find an signal for every type of action thus there is actions that would signify two body motions

Difficult to understand, Long Conversations not possible and it will build communication gap.