A Location's Review Frequency is used to set a default date on all Items added to the Location that do not have an definite set action date without having to add an action date to each individual Item. It is a good way of ensuring that you are always on top of your items by receiving a reminder to review or take action.
You can set Review Frequency to a specific date or for a specific duration. A specific date will mean that the frequency will expire the day after the set date and will need to be reset. Setting a duration means that the item's action date will be set to the date in respect to the duration, like two weeks from the day, or 6 months, etc.