It has a enormous impact, you can take that for granted. Different cultures use different body language to show respect, for example. Here in the English world we expect someone to look at us when we are speaking to him, refusal to do so is a statement that the speaker is being ignored. But Hispanic women lower their eyes when a man speaks to her, out of respect. Misinterpreting things like this is a real headache.
In India people (the common people at least) squat all the time. I realized that by standing while they were squatting led them to believe that I held myself above them out of arrogance. And, it was true.
People from India nod their heads side to side to indicate approval, and up and down to indicate disapproval.
To really understand this you should read a book about basic cultural anthropology.
