If my memory is correct, it's a vacuum control solenoid to control the vacuum advance for meeting smog regulations. I think it was for limiting in high gear if the distributor received full advance, near as I remember. It may have been controlled/limited by coolant temps. I'm trying to recall from 50 years ago, when I graduated from high school, and began my trade as a mechanic, so it's not right at the forefront of things I recall. It's location was on the rear of the intake manifold, close to the vacuum advance can on the distributor.
It was one of the first things that got bypassed if you wanted full advance all the time. I do remember that.....
it usually was never removed from the engine, just taken out of the vacuum routing. Just like what you have shown.
If I remember correctly, there was a small foam rubber filter on one of the fittings that was exposed to atmospheric air, they deteriorated within a few years of under hood temperatures.
I hope that helps answer your question.