MikeE,
The voltmeter will show you that your system is charging and will show the approximate state of charge of the battery. This is usually enough to make the average Joe comfortable. If you need to see how much current various items are actually drawing then the ammeter is for you. You will probably never ever be able to 'fry' your voltmeter, and being tagged into the system the way it is, you don't end up with one meter passing all the power, which some consider dangerous.
I think this is sort of a personal preference kind of deal!
Stuart
