A history of heights in Canberra
It's also a great advantage if the heights are all relative to one known point; usually mean sea level, rather than a series of dispersed benchmarks that might not agree with each other.
When the Canberra-Queanbeyan area was selected as the site of the national capital and a competition was set up to choose a design, the planners needed a topographical map.
This was provided by detail and contour surveys done during 1910-13. As more and more data became available, height information was progressively improved and integrated.
This paper, by former Australian Survey Office surveyor Peter Daly, gives a potted history of level datums in the ACT and some of the processes of integrating data from different eras.