Using relationships vs merge join difference

Hi, 

When working with a couple of huge files (SQL-DirectQuery) I got the error that there was too little memory to show the matrix when choosing 'Show items with no data' for the linked tables. 
When I didn't choose 'show items with no data' the relationship only showed values from the first table with related values in the second and third tables (practically making it an inner join relationship).
Using a left outer join when merging queries solved it.

Don't know if there is a fundamental advantage in performance when merging, compared to managing your relationships.
I guess there is more choice when you merge, because you can choose:
Left Outer, Right Outer, Full Outer, Inner, Left Anti, Right Anti 
and when you manage relationships, you can only choose
many to one, many to many, one to one and one to many.

Grtz