By default, vBulletin stores all data in the database. This default is for convenience instead of performance. To allow vBulletin to perform better, you can move the storage of attachments, avatars, CSS and templates to the file system.
These settings are configured on vBulletin Cloud sites by default. Cloud Site owners will not be able to make these changes.
With a default installation, vBulletin will build and serve the CSS along with standard templates. This uses a redirect to the /core/css.php file. To improve your site’s performance.