What is the significance of post title to the url?

When I asked something in stackoverflow or in Quora, I see that that whole whole question title into the url. And in stackoverflow its like .../questions/id/question-body.
My questions:

• why question's heading to the url?
• is there any security issue to add id only to the url? (like: http://ift.tt/2nhYpJM)
• or adding question just to give users some extra feedback(on that case the its a silly question at all).