A duplicate creates a separate copy. Changes made to the original no longer work in the copy.
A reference creates a link. Changes to the original also affect the referenced query.
Neither impact the utility of a Star Schema. They are just how you get there. You want the most efficient way possible. I rely a lot on references and less so on duplicates, but that doesn't mean references are better. I think they are better for the places I use them in. But I will use the duplicate feature for some models.
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DAX is for Analysis. Power Query is for Data Modeling