ExecuteWorkflow is used to move the workflow request to the next status. This is useful and important since this is the only way to make the workflow move forward unless you set the workflow status to run automatically.
Each workflow status has three processes - StatusArrival, CompleteStatus and StatusExit. StatusArrival and StatusExit run automatically once the workflow request reaches and exists this status. However, CompleteStatus only runs when ExecuteWorkflow is called.
ExecuteWorkflow service is generally used in button processes, stand alone processes deployed as scheduled tasks or workflow StatusArrival processes.
If you have any question about EASYProcess workflow, please refer to the Workflow document for further explanation.