Small vacuum manifold connection?

1970 S2 reassembly is progressing. I note a small vacuum connection on the rear end of the intake manifold between the big vacuum pipe for the brakes and the water connection. Is anything connected to the small vacuum pipe? I have it caped off at the moment. Could it have been for vacuum retard to the distributor?

That vacuum connection is attached to the vacuum switch on the back of the air filter housing.The distributor vacuum is connect to the underside of the front carb.