This function is commonly used when there are more than six modifier groups assigned to an item, as you cannot assign over 6 groups to a menu item. This will link the Modifier Group you are currently on to another modifier group.
AUTHOR NOTE: program menus that are simple for end-users to make changes. At no time should a menu item have over 6 modifier groups attached to it. It’s unnecessary and expends more of the order taker’s time.