I have always wondered why animals use terrestrial locomotion?  Why don't they just disappear and then reappear wherever they want to be?
It is definitely an interesting topic! I believe the way the body is supported by the legs is an important part. 
Yes, my appendages are certainly helpful in giving me an upright posture.  However slime molds also move, and they don't have legs.  They must be teleporting, right?
I find it interesting that certain animals have different posture's depending on the situation