Imagine we have boards A and B. On board A we have an item, on board B we have three items. Board B, three items connect to the item on board A. This is the standard high/low-level board.
The new connection type is “shared” where the three items on B being connected to the item on A - implies an item on B is also connected to the other two items on B.
Use case: status sharing to completion of a group of tasks being made visible on both the high and low level board. That way on the low level board we can see progress on all tasks related to the effort on each item as well.