I am wondering if any reason other than the user friendly presentation to use the clean URL and Pathauto .
I had search in Drupal.org, wiki and Google, the two reasons found are to improve the SEO and security issue.
But I notice that those passages saying to improve SEO were coming from third party.
In Google or Yahoo official website, I cannot find any information about how Clean URL affect the SEO.
If any, please kindly let me know.
Beside, I would like to know the security risk/issue when using the real URL.
I assume the security issue would only apply to static html website.
For Drupal, it is dynamic URL structure with permission control (or Content Access module).
Therefore, I think the security issue is not applicable in Drupal.