Map light switch

Hi All:

I've got an owners manual and service manual on the way from Faxon, so hope I don't have to ask a question this dumb again....lol.

On my car, there is a map light switch on the bottom of the dash beside the hood release. Unfortunately, the switch seems to need replacing....it doesn't move very easily and doesn't seem to do anything. What the heck is this this for? I've seen maplights on B bodies before that turn on a light under the dashpad, but I looked at my car and I can't see a maplight under the dashpad. If this switch turns on the dome light, I'm wondering what's the point, because turning the headlight switch all the way will also turn on dome light.

So....what the heck is this thing for?