Groundspeed allows you to modify the forms and form elements loaded in the page. Some practical uses include:

Changing the types of form fields, for example you can change hidden fields into text fields so you can easily edit their contents.
Quickly removing size and length limitations on text fields so you have more space to type your attack strings.
Changing form target so the form submits in another tab.
Removing or editing the JavaScript event handlers to bypass client side validation.