Google is smart enough to highlight the search term that appears in the title and the url. This “bold” part in the link easily catches users’ attention and also leads them to believe that the link will more than likely points to the content they are looking for.

Compare the 2 links below:
http://www.site.com/index.php?main_page=product_info&cPath=40_44&products_id=506

http://www.site.com/toyota/prius/2009-toyota-prius-hybrid

Which link is more “readable”, which one tells you exactly what to expect when you visit it? Obviously the second link is more meaningful to user. You know the content you should see when you visit that link.

Shop owners also reported that using this user friendly url can help them to save a huge amount of time when they track their site traffic via Google Analytics or other statistic tools. By just looking at the links they can know exactly which products/categories those links point to without having to actually visit the links.

Usability

Lets  say you start with:
http://www.site.com/toyota/prius/2009-toyota-prius-hybrid

What if you want to go and see all cars listed uner “prius” category? Simple, remove the product name from there:
http://www.site.com/toyota/prius/

What if you want to view the “toyota” category instead?
http://www.site.com/toyota/

Most users won’t do that, they will follow the navigation bar on your site, but some will try. And it’s good to give them the option. It’s also nice to let them know exactly where they are by just looking at the links.