Summary: Shortcuts, unseen by the novice user, speed up the interaction for the expert users so that the system can cater to both inexperienced and experienced users.
Flexibility and efficiency of use are about allowing users to approach tasks in a variety of ways. New users may require guidance in fulfilling their tasks, while experienced users can benefit from accelerators and secondary features designed to speed up commonly performed actions. Flexibility and efficiency of use ensure user customisation and provide accelerators to empower users.
Link to poster with tips & tricks