Vacuum advance units are a bit like thermostats. Your car will run without it, it will run for years without it, but it will not run at it's BEST without it.
Thermostats & Vacuum advance units cost the manufacturer money to make & install, and our cars were competing in the low cost end of the market where every dollar counted, yet the manufacturer still put them in.
They did it for a reason, a very good reason.

When you are operating at light throttle & at cruise speeds, the manifold vacuum is high, so the vacuum advance kicks in & allows the meager amount of fuel that is being admitted to the cylinders to be ignited at the right time & to provide the best power result at this throttle setting.

If the vacuum advance is not kicked in, then the engine's ignition timing is effectively running retarded from the optimum position, requiring more throttle opening to maintain the desired cruise power setting.

End result, ... increased fuel consumption at cruise power settings, so I suggest that you make the effort to find a serviceable unit that is correct for your car & maintain your pocket rocket properly.