"You have a good career."
Translation:Kamu punya karier yang bagus.
I found this article useful: https://blogs.transparent.com/indonesian/the-us-of-yang/
I think they want to put emphasize on the adjective; that it is a good career.
If the sentence were something like "His good career had no influence on his decision" (no emphasis on the goodness of the career), you can leave out "yang".
I'd say, in this case, "with 'yang' is stilistically much better, but without 'yang' is not outright wrong"....?