1
general::
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.
American Heritage Idioms
2
general::
Phrase(s): serve a (useful) purpose
to be useful in accomplishing some purpose. • This large book should serve a useful purpose. We can use it for a doorstop.
McGrawhill's American Idioms And Phrasal Verbs