Why may need to have more than one relationship between the two tables?
I don't understand why we have to have two relationships between two tables.
One key is not enough to link two tables?
I think you said this issue too early and I wish you would have left this issue after we became a bit more professional in PowerBi.
This is because you might be in a situation where you want to build measures for ShipDate and OrderDate. They require separate relationships to the dimension date table in order to build the time intelligence functions. It is not always necessary to have multiple relationships, usually one active relationship is enough, but in case you need more than one use the suggested solution.