I will give a real life scenario I faced:
In my website: http://www.bestwebhostingsites.org/
I tried adding a hyperlink in one of my blog posts. So, I pasted this in the URL box of the visual editor: http://www.bestwebhostingsites.org/bluehost
WordPress neither corrected this error nor prompted me to do so. But luckily enough, I happened to check the final (published) output which turned out to be like this: http://www.bestwebhostingsites.org/www.bestwebhostingsites.org/bluehost
I tried finding the error but it was very difficult to find. It was only after spending 1 hour that I realized that http:// prefix was missing in my URL which was resulting in all this.
Can't we have an arrangement through which the initial http:// is automatically added by wordpress whenever it is missing.
I tried experimenting this in MS Word and found that it takes care of this problem so well. In fact, you can never have this error in MS Word.
How nice it would be if we could have something similar in WordPress as well!