Have you ever looked for missing remote server names, user names, and passwords? Have you ever tried to transfer a site definition to another system by copying the data stored in the Site Definition dialog box? If so, you probably discovered that it doesn't work because the password is encrypted.

Fear of losing user names and passwords is but one reason to back up your site definitions. You should also back up your site definitions each time you add a new site or edit an existing site because your computer could crash and you might lose your data, or something could go wrong when you install an upgrade or update that causes you to lose your site definitions. Backing up your site definitions also safeguards you against an occasionally-temperamental Dreamweaver installation that might "forget" your site definitions.