From RPGSite: "Bravely Default II has a plethora of complicated systems and mechanics, but one of the most curious is the Exploration system, where you send a boat to explore, and get certain rewards. Exploration is a handy way to get some decent, useful items while you're not playing the game - and so you'll definitely want to engage with this system.
That's right, by the way - we said while you're not playing the game. The Exploration mechanic in BD2 is rather like the sort of thing we typically see on handheld systems and mobile for the most part - which makes sense, of course, as though this sequel is on the hybrid Switch, it began life on 3DS. Basically, you let your characters go out 'exploring' while the game isn't being played, while your Switch is in sleep mode, and they return with items"