If your lawn contains islands with a small diameter (up to 2 meters), then you can leave the setting of the ‘Islands’ to ‘Off’, as the mower will detect such an island, and will leave them fairly quickly.
But in cases where there is a large island (for example a swimming pool, pond, or a large group of flowers/trees), which the robot can drive around for a long time, then it is recommended to set the ‘Islands’ to ‘On’, in order to prevent the mower from following the wire around these islands.