N cardinality collection link use

Hello,

I´m trying to understand better the different type of relations that can be set between resources in ACS.

I understand "1 cardinality simple link" and "0 or 1 cardinality simple link", but i am having some trouble with "N cardinality collection link"

Adobe´s videos about defining custom resources say that this link is the opposite to the "1 cardinality simple link", but with one difference: it´s mandatory that one row from the source resource is linked to a row in the target resource.

I made some tests creating a "Orders" resource and also a "Order lines" resource, and defining a "N cardinality collection link" from "Orders" to "Order lines". I was able to create some orders not linked to any order line, so i don´t really understand why Adobe´s documentation say it´s mandatory that every order (in this case) has to be linked to an order line.

Does anyone has an example when using this type of link is useful rather than using a "1 cardinality simple link"?

Thanks and best regards!

Mario