A definite predicate can be useful when the speaker connects a previously identifiable relationship or person with the subject. It may answer a question of identification rather than merely assign a broad quality.
«زيد أخوك»
Zayd is your brother.
«عمرو المنطلق»
ʿAmr is the one who departed.
«أخوك» is definite through annexation, while «المنطلق» is definite through the article. If the hearer wishes to identify the person who departed, the latter formulation can supply that identification.
Definiteness and exclusivity are related in some contexts but are not identical. A definite predicate does not by itself always establish an absolute restriction.