From the article:
A staff team is an important component of large artillery platoons. The staff team's job is to take the target's map reference, radioed to them by the spotter, and convert it to angles and elevations for the artillery weapons.
Their technical expertise allows the staff to perform complex calculations and communicate the results to the rest of the artillery platoon quickly.
Mortar platoons and rocket batteries lack artillery staff because their operation does not permit prolonged bombardments and sophisticated artillery tactics.