There's something you need to do when someone arrives at or leaves some place. Unfortunately, you don't know when that will happen. Currently, Reminders will only alert you at a specific time or when you arrive at or leave a predefined location. My idea is this: if Find my Friends can notify you when a friend arrives at or leaves a predefined location, then Find my Friends should be able to notify the Reminders app when that event occurs, too. Scenario: Bob wants to be reminded to give Jill some money when they meet. Since Jill has given Bob access to her location via Find my Friends, Bob can set up a reminder in his Reminders app so that his phone reminds him when she arrives.