One needs some sort of altimeter setting, and not everywhere has a convenient H24 ATIS broadcast.
Rather than the UK's RQNH, I prefer Oz's Area QNH. The difference is that AQNH in Oz isn't the *lowest* for an area but is more like a QNH expanded to cover a large area accurate to within a few mb. If the difference becomes greater than 5mb then the area is subdivided to make sure there is never more than a 5mb step from one boundary to the next.