Flag Recommender uses the Recommender API module to calculate recommendations based on user flagging activity. For example, using the default "Bookmark" flag it can calculate two types of recommendations:
Role Vocabulary will sync all user roles as taxonomy terms in a particular vocabulary.
This is particularly helpful if you are using something like Taxonomy Access Control Lite and have a taxonomy which you use to define access to particular pieces of content per role. Role Vocabulary will keep these taxonomy terms up-to-date.