serve a purpose - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Also, serve one's or the purpose. Be useful, meet the needs or requirements, satisfy, as in I don't know why they've added all this information but it probably serves a purpose, or It often serves his purpose to be vague, or We don't have a spading fork but this shovel should serve the purpose. This idiom was first recorded in 1513.