What role does the RewriteBase directive play in Joomla's .htaccess file, and how does it contribute to 500 errors?

The RewriteBase directive tells the Apache server where to start looking for URLs in the site. Incorrect RewriteBase settings are a primary source of 500 errors, especially after moving a Joomla site to a different directory or subdomain. Incorrect RewriteBase directives will cause loops or incorrectly rewritten URLs that will cause internal server errors. For example, if the Joomla site is in the root directory of your domain, the RewriteBase is usually '/'. If installed in a subdirectory, it should be '/subdirectory/'.