The Step property allows you to change the step at which Series Labels are displayed. By default, the Step property is set to 0, so series labels are displayed for each series. Below is a chart with the Step property of the Series Label set to 0.

If you set the Step property to 2, the "Series Label" will appear as shown below.

A value of 1 for the Step property indicates that a SeriesLabel is displayed for each Series value.