It can be very useful if a form is preloaded with the entire content of a page, except for some fields. This could be done with a #formlink in which both the preload parameter is used and separate query string parameters.
An example of this is it is: {{#formlink:form=Order |link text=Make copy | preload={{PAGENAME}} | Order[Customer]= |Order[Name]= |Order[Order number]= }}.
This would take you to the Order form, preload all fields with those from the current order except for the Customer, Name and Order number field that remained empty. The order number could get the default value as defined in the form and the name and customer can be entered for the new order.
In Page Forms 4.1 the preload of the whole page works fine but the other parameters have no effect.