Serve a, his, its, etc. purpose - Idioms by The Free Dictionary
serve a, his, its, etc. purpose
serve (one's) purpose
To fit or satisfy someone's requirements; to be useful for or fit to achieve someone's aim, goal, or purpose. Well, it isn't a very pretty car, but it should serve our purpose just fine. Child: "But mom, I want a smartphone!" Mother: "Nonsense, the cell phone you already have serves your purpose just fine."
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.