It may be useful to have a form pre-populate with certain data elements. For example, you may want to default an Employee Name field for a human resources form to a specific Employee. One way to achieve this is to include the data in the URL link to the form. If you are integrating access to forms into another line of business application like Salesforce.com, you can even pass application data in external URL's making this approach very useful.
To get started, you must know what query string parameters will be passed in the URL to the form.
Example Form URL