Search volume tells you that people searched. It does not tell you whether search helped. Product teams need a small set of measures that reflect both customer effort and business outcomes.
Track successful search sessions, reformulation rate, time to useful action, and the downstream outcome appropriate to your app. That outcome could be adding an item, reading an answer, booking a service, or completing a workflow.
Segment these measures by intent and entry point before comparing trends. A broad exploratory search should not be judged by the same standard as a known-item query. Document each definition so teams interpret changes consistently.