The SmartFavorites system attempts to learn which folders you most often use and display them in the Favorites menu automatically. You can also optionally show them in the folder tree.
SmartFavorites are based on a points system. A number of points are allocated to certain activities that are performed in folders, and Opus keeps track of the points that individual folders have earned. When a folder's points exceeds a configurable limit it is deemed an important folder, and will appear in the SmartFavorites list.
At the bottom of the page is a list of activities. You can adjust their points values here if needed.