Let's say you have 2 drawers (horizontally or vertically next to each other) and you are using a grained board.
In order to make sure a grain flows correctly, you need the drawers placed vertically next to each other on the optimisation layout.
When optimising if the optimiser could handle both panels (Based on Link Placement of whether they are next to each other vertically or horizontally and then when generate the optimisation make sure they are grouped next to each other.
In this situation they would need to be vertically linked.