When developing for vBulletin or troubleshooting issues, you often have to enter Debug Mode. Debug Mode provides you with more information about how vBulletin runs some examples include: page generation times, templates used on a page, the memory used on a page and how many queries it took to generate the page. Debug Mode should not be used on a live production site unless absolutely necessary. It can expose information that could weaken security on your site.
$config[‘Misc’][‘debug’] = true;