The favorites sidebar lets you browse your favorite folders for archives. All other files are filtered out by default. BetterZip uses macOS’ Spotlight index to quickly find and keep track of all archives inside your favorites folders. That means this feature will not find archives in folders that are excluded from your Spotlight index. See System Preferences > Spotlight > Privacy.
To open the favorites sidebar choose View > Favorites, click the favorites button in the window’s bottom-left corner or press ⌘B on your keyboard. Hold down ⌘ and click an archive to open it in a new tab, hold down ⌥ and click an archive to open it in a new window.
Right-click items in the list for additional file management actions. The contextual menu also offers an option to disable file browsing in case you want to use the sidebar only as a drop target for extraction similarly to the Finder sidebar and an option to hide the archive count badge which may be used to save some space and make the sidebar narrower.
To open an archive from the favorites sidebar simply select the archive. It will open in the same window. If you already have an archive with changes opened, you will be asked to save your changes first.