Should I run the VSP Engine Tools in asynchronous mode (default) or in synchronous mode? What is the difference?

ERSI Geoprocessing Tools can be executed asynchronously or synchronously and should be configured according to their purpose and expected execution durations. Since printing/exporting tasks are typically long-running tasks compared to other geoprocessing tasks like data analysis, the VSP Engine Tools should always be run in asynchronous mode. This is also the only mode supported by VSW.

A primary functional difference between a synchronous and an asynchronous task execution is that and asynchronous task creates a job ID as soon as a task is submitted by the client, and then is frequently polled until the results are available. The task's scratch workspace can be found in the configured service jobs directory on the ArcGIS Server in a folder named by the created job ID.