Meaning of fourth option when selecting furniture in room?

When you click on an item of furniture in your room what does the new fourth option mean? (Looks like white tiles)

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I just checked in my own game to see what this option does.

Rather than place a grid on the ground as others have suggested, it makes moving the object you're trying to place much more "snappy." Instead of freely moving around, the object will move by set distances in whatever direction you try to move the object. This is to help you align objects you're trying to place when decorating your room.