What is the difference in Robomow behavior when the islands are set to ON/OFF?

Islands OFF
Usually recommended for lawns without an island installation.

When the mower is in searching for Base Station mode, the mower will acquire the first wire it detects and follow all the way to the Base Station.

Island ON
This is recommended for lawns with island installations.

In rare cases, you may notice that the mower unnecessarily circles around a Perimeter Island while searching for the Base Station. The Islands option helps overcome this situation. To avoid such cases, turn the Islands feature On.

When the Islands feature is set to On, the mower will execute a special method of searching for the Base Station. As a result, it may take the mower longer to arrive to the Base Station.