I have a topical fluoride tray system in my office. What would be the advantage of adding a fluoride varnish as well?

Topical fluoride varnishes [Duraflor (MEDICOM, Inc.)] can be used in young patients who cannot tolerate fluoride trays for caries prevention. Varnishes can also be used to reduce postoperative sensitivity after an in-office bleaching procedure, and to treat dentinal hypersensitivity.