Kitchen design rule 6 - minimum distance between kitchen benchtop and island. We were planning to have it attached but we dont see the point really. Also fixed islands require electric per most US based municipalities while floating doesnt have any requirement.
If they have the option to do so they will fasten it to solid blocks of concrete in the floors.
Design the moveable island bench so it can easily be wheeled into the main. If it is an island you have two options. Design the moveable island bench so it can easily be wheeled into the main. Smaller kitchen islands should be secured to the floor so they do not slide or tilt if someone leans or pushes against the island.