Surveyors use them to measure elevation.
I use them as a way to measure my relative failure or success. Lately in the library I've developed a few new ones. For example, any day when the police don't come and there are no bodily fluids on the floor or furnishings is a good day. It's incredibly easy to have a good day when you're keeping it all in perspective. It just depends on where you put your bench marks.
