serve a, his, its, etc. purpose

serve a, his, its, etc. ˈpurpose

,

serve the ˈpurpose (of doing something)

(British English also serve his, its, etc. ˈturn) be useful for a particular purpose or period of time; be good or useful enough for somebody: It’s not a very good radio, but it serves its purpose.He used his friends and then abandoned them when they had served their turn.
See also: purpose, serve