The debug capabilities of Cartweaver 4 are a powerful tool to help you test your site and track down the cause of any problems that may occur. During development, you want to know what is going on and have as much diagnostic information available as possible. On the other hand, once your site is live, you don't want to present this debugging information, otherwise know as ugly error screens, to your users. The debug settings on this page will help you control this.
During Development and when tracking down problems, you may want to disable by un-checking "Enable Error Handling" and selecting the rest of the fields on this page, so the full error information will be displayed in the browser.
For your live site, you should consider enabling error handling - this will present a custom error page to your users that can be customized to look like the rest of your site and present a more user-friendly error message.