When necessary.
It depends. By default I would advise against them; not creating Form objects to receive and validate data that could be validated by the Model directly. Even when you have a few nested attributes that belong to the main model modified, I would advise against Form objects. Keep It Simple.
But… sometimes you have more complex forms that don't fit the database-mirroring model as nicely.
Dit artikel van murblog van Maarten Brouwers (murb) is in licentie gegeven volgens een Creative Commons Naamsvermelding 3.0 Nederland licentie .