I just started mine for the first time since it went into hibernation this past winter. Normally it would take forever to work the fuel back into the carburetor but I installed a Sniper EFI last year. Fired right up!
I believe it is to help relieve cabin pressure quickly, like when you are closing the door. Also, when the windows are up and the blower fan is on pulling air into the car for heat and a/c, the old air has to go out to allow for flow.