Only use for vacuum I can think of would be 1. Wipers, 2. Hydrovac or vacuum assist brakes, 3. Vacuum Primer for a fire engine.
On my trucks, the tube you're describing is a seperate piece below the carb, basically an insulator with a tube stuck into it, not actually part of the manifold. No reason you can't remove it if it's not being used, though I think you'll need shorter studs for the carberator to bolt to then. Not worth the trouble, in my opinion. Just leave it plugged. Tell people it's the blinker booster!
-Michael
