[glenra]

Somebody with poor eyesight and slow reaction speed is an unsafe driver but doesn't need any particular help loading/unloading from a car. A driver who can help unload is a fine thing, but having somebody drive just so they can help unload seems like a ridiculous waste of resources. A car is ready whenever you need it; a car-and-driver might not be. And yes, you could schedule a car-and-driver to be available at a particular time...but you could similarly schedule somebody to be available to load/unload at the destination.