The foam boards, most likely pink in color are called Rafter Vents (owens corning). They are in integral part of the ventilation system in your attic to keep your house cool/warm in the correct seasons. Also adds to the longevity of your roofing shingles etc. They also can help prevent Frost/water ice dams from occurring under the shingles in cold weather. So when he tells you they're not needed?? you need to think of what else he doesn't know.
The rafter vents slide in between your rolled in or blown in insulation at the base of the roof line leading to the soffit in between each or the roof rafters. They "push down" the insulation just enough to give you an air space for air flow between the interior of the roof and the soffit. (Make sure he uses vents in your soffit and not just side wall vents). Air flow is important.