This feature is used to change the spacing between items in a layout so they can be closer together or further apart.
For example, four individual single-sensor cameras that together form a 180 degree panoramic view would best be displayed without any space between cells.
To adjust the distance between items, open the Viewing Grid context menu and select Cell Spacing, or use Ctrl+Mouse Wheel over the Viewing Grid. Options are None, Small, Medium, or Large.