He's referring to the PCV system. That hose might actually hinder performance slightly, since at boost it tends to draw some oil into the intake line. It's recommended that hose be routed to the intake, or to some sort of breather setup to pull in air to keep the crankcase pressure down.
Unless you mean ABOVE the valve cover, that hose runs to the Wastegate diaphragm on the turbocharger, slightly under the exhaust manifold. They may have rerouted that for a boost controller setup.