What is the use of "Exclusion" relationship in relationship type?

I find it hilarious that I’m mentioned before the "official" Aras employees. I’m not exactly popular at Aras, but I am happy to have the trust of the community [emoticon:d6dd260102fd406884fc96b8bc59760b]

Otherwise, the official documentation (Online help!) explains this case best:

Exclusion - Sometimes relationships may be mutually exclusive.  For example, you may have a relationship such as a BOM for a part, and a relationship such as Vendors for a part.  However, the part is either made in house, in which case you would need a BOM tab, or it is bought from a vendor, in which case you only need a Vendors tab. So, on the Exclusion tab you can specify a list of relationships that are mutually exclusive.  In this example, in the RelationshipType for BOMRel, you would specify VendorsRel under the Exclusion Tab.

This technique isn´t used very often. Aras e.g. uses it in RelationshipType "RelationshipType"