Show where variables are used in workflow
Within the variable menu you should be able to see where a variable is being used (what actions) within the workflow.
If you need to find and replace a variable within the workflow designer (such as needing to change a variable's type), when working with large workflows it is hard to find where the variables are being used, but you cannot update/remove the variable until all instances are removed from existing actions.
Anne Collier commented
The ability to search for variables or text within the workflow would be really helpful too. Search and replace would be even better.