Forum Moderators: DixonJones
If the URL is a folder, then the server should normally issue a 301 redirect from "without" to "with".
If the URL is for a file, then "without" should serve the content, and "with" should issue a 404 error.
More information should be gleaned from your server documentation (Apache, IIS, etc - WebmasterWorld has a forum for each of those here) before making any changes.