What Are 'Clean URLs' and Why Do They Matter???

Old (dirty) approach to a URL: http://www.myapplication.com/App_v2/User/Page.aspx?action=show%20prop&prop_id=82742

New (clean) URL:  http://www.myapplication.com/to-rent/chicago/2303-silver-street

Why Are Clean URLs important?

1. Search engines give considerable weight to keywords found in a URL. A search for "rent in chicago" is much more likely to turn up the latter URL. 
2. Many web users are now savvy enough to understand a URL, and appreciate the option of navigating by typing into their browser's address bar. 
3. When someone feels they can understand a URL, they're more likely to link to it (being confident that it doesn't expose any of their own personal information) or share it with a friend—perhaps reading it out over the phone. 
4. It doesn't pointlessly expose the technical details, folder, and file name structure of your application to the whole public Internet, so you're free to change the underlying implementation without breaking all your incoming links.