The Standard deviation is a simple measure of the spread of ratings score/data.
It provides a story behind the data/runs, without actually having to explore all the data/runs.
Once you explore this concept you will find most starters conform to a Normal Distribution whereas 1 stdev from the mean encapsulates 68% of a runners starts, 2 stdev equates to approx 95% of a runners starts an so on.

In greyhound racing cause they run so consistently its easier to show how you'd use this data.

say we have two dogs Dog A)mean time of 31.55 with a Stdev of .141 Dog B) mean time of 31.62 with a Stdev of .176

Now if you were just comparing these two dogs Example#1 Dog A runs an average race, then what is the probabilty of DogB beating him, we can do the following (31.55 minus 31.62)divided/ .176 this provides you with a zscore of -.398, now all you need to do, is a search on the net or use excel formulas or find an in any introductory statistics textbook an from that zscore table you will find the answer being .3446 that means when Dog A runs an average time Dog B will beat him 34.46% of the time, then you just reverse Example #1 to find when Dog B runs an average race whats the probabilty of Dog A beating him 31.62-31.55)divided/.141 =.496 look up the zscore table an the probabilities of Dog A beating him is .6915 or 69.15% of the time.

Now you would take this a step further by knowing what was the average rating to win todays race so you would substitute one of the above examples by this new avg win rating.

To further refine the above you would then say make an adjustment to say Dog A mean score if he has drawn box1 in todays race but in turn his Stdev would become tighter as his performances would be more consistent..an so i hope you can see the power of just using Stdev..