Population Standard Deviation

So we know that the population standard deviation $\sigma$ is just the square root of the variance $\sigma ^2$. But what are the uses of the standard deviation? At this juncture it just seems are random variable to me, but what are the uses of the standard deviation?

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I believe standard deviation is used rather than variance to make units consistent (variance is in square units, by virtue of how it is calculated). –  Daniel Littlewood Nov 18 '12 at 17:07