Form Data Fields
Form data fields are used to store data that is needed only for the lifetime of the form.
User task parameters offer a way to associate a user task with process data fields so that data that is available to the entire process can be used, viewed, or modified through the form associated with the user task. But in some cases, you want to track data that is useful for the functioning of the form, but is unrelated to other tasks in the process and is not needed by the server. In such a case, instead of using parameters, you can create one or more form data fields to store that data for the lifetime of the form.
The same data types available for parameters are also available for form data fields. The key difference between a form data field and a parameter is that a form data field has no Mode property (In, Out, or In/Out). Since a parameter’s Mode property is used to specify the way parameter data interacts with the larger business process, it has no relevance to form data fields.