You can have as many PST files as you like showing in the Navigation Pane at one time. For example, you may be reading archived messages from years ago in one PST file, and reviewing messages about a current project in another.
Earlier we mentioned that having too many PST files open at one time will slow Outlook's performance. If you no longer need to review the contents of a PST, you can remove it from the Navigation Pane. You would do this by right-clicking it and clicking Close "Personal Folders" or Close "Archive Folders" or Close whatever unique name you've given to your PST file. (You'll see later in this course why unique names are a very good idea.)
Closing a PST file keeps it from being displayed in Outlook, but it doesn't affect its contents or its location on your computer. And you can always reopen it by following the steps we mentioned earlier.