[theophrastus]

Or why use variances when there are standard deviations (the square root of the variance) which have more easily interpreted units? One commonly cited reason is that one can sum variances from different factors, which one cannot do with standard deviations. There are other properties of variances which make them more suitable for continued calculations[1]. This is why, for instance, variances are often utilized in automated optimization packages.

[1] https://en.wikipedia.org/wiki/Variance#Properties