This function allows you to scan the source files before starting the backup job, according to file filters, and find out which files will be copied, which ones have been modified and deleted, compared to the previous backup. In addition, Preview displays very important information - the path of each file inside the future backup. This way you can see the directory structure inside the backup (in the destination folder).
To start scanning, click on the "Preview" button located on the top bar in the main window.
NOTE! File scanning is a secure feature that does not copy or modify files on the drive.