Yes, a good point. It seems IE5 was actually ahead of the game at the time 
To be honest I don’t often find the need to use calc other than in edge case demos but there are a couple of places they can be useful if especially you are using the content-box model (the standard model).
e.g. If you want two floats next to each other but one is a fixed width and both have padding and borders then you can’t do it without using calc (there are other ways of doing this without using floats so assume floats are requisite).
Calc has also being used for responsive text resizing.
Calc is just another tool in the toolbox that comes in useful when you need it.