What potential pitfalls should be considered when setting up multiple URLs with .htaccess redirects in subdirectories for PHP sites?

When setting up multiple URLs with .htaccess redirects in subdirectories for PHP sites, potential pitfalls to consider include creating infinite redirect loops, causing 404 errors, and impacting site performance. To avoid these issues, it is important to carefully plan and test the redirects to ensure they work correctly and do not conflict with each other.

RewriteEngine On
RewriteBase /

# Redirect old-url to new-url
RewriteCond %{REQUEST_URI} ^/old-url$
RewriteRule ^(.*)$ /new-url [R=301,L]