I've seen it for quite some time. Say you have no tangable way of tracking conversions accurately. You could use this as a way of at least getting some sort of data. For example, say you have a contact page with no submission form. Just your address, email and phone number. After browsing your site for a while the customer may want to make a purchase by contacting you. They will navigate to the contact page. Since this is important and implies a potential lead, you may decide that this is an effective enough way to track a conversion.