Before for example making changes to a Step Definition it is a good idea to see what the impact of the changes will be. A way to find out is to click the 'Where Used' tab on the Step Definition. This will show the Flow Definitions that use this Step Definition.

On the Part and Traveler tabs you can see the parts and Travelers that are currently in Steps using this Step Definition.

It is possible to make changes to an Active Step Definition by moving it back to Pending, but for bigger changes it is recommended to use the Revision Control features.