If we have a long running workflow tasks or have a  large number of workflow tasks executing , we can unload and store it in a temporary storage using Persistence services ships with Workflow Foundation.

Dehydration : Removing a workflow instance from execution status and storing it away for later recall is called Dehydration. Typically persistence services that comes with WF is used for this purpose, but you can write your own service to perform the same task.

Rehydration: When needed – the workflow instance is brought back from persistence service. The process of bringing it back into an execution status is known as Rehydration.

The main goal is to unload the long running tasks from memory and store then in temporary storage and retrieve it when its needed. And by this way – it’s possible to provide efficient memory utilization.