The old style CH ignitions, with the rubber boot that I have, the wire braid shields are all grounded at the cap. And if they are not grounded, the spark is likely to jump somewhere else and cause trouble. I have one CH with a shielded cap (Bosch-Mercedes Benz) but the shield grounds at the spark plug, not the ignition module.

Even on a RCEXL ignition, if the cap comes loose while the ignition is running (sparking), The spark will jump inside the sensor instead and take it out.