Abandoned Cart is a good example. It takes the email address if it's been filled out and auto-sends a reminder email later.
Not really the same thing as taking your payment and address information and sending it to some guy in a basement. Half-complete or incorrect data isn't an issue any company wants to deal with. Abandoned Cart functionality makes money, so that's why it's included.
Another use is for a form with questions, like you get in jobs postings. Seeing how someone types in the answers may be more revealing than the answer itself.
The closest thing I can think of is as an "abandoned cart" for forms.
"You were about to submit our contact form to ask about our software. Are you still interested in a demo? (we're evil, by the way)"