On the Stovepipe Systems blog Iltar van der Berg shares some thoughts about rethinking form development and how moving from composition over inheritance model can help make working with Symfony forms easier.
In one of my previous blog posts, Avoiding Entities in Forms, I've shown how to decouple your forms from your entities. Afterwards I got feedback and most of it was about the lack of examples and the flow, when to fill your data and how to get this back in the entity. However, often I notice that developers design forms based on their entities. This can lead to complex forms because you're confined to a strict set of properties. Developers often get struck with unmapped fields and form events to work their way around those limitations.
With Symfony Forms I highly recommend to follow the composition over inheritance principle. Small form types are easier to re-use and make it less complex to build forms. Moreover, this allows small data objects to have specific goals with validation for their specific case, rather than complex validation groups.
He starts with an example user story, defining a need for a form that allows users to post comments on blog posts. He starts on this simple form, defining the "bare minimum" the form requires and creating a class/entity to match. He then talks about what happens when the business need changes and they want a checkbox too. Since he created the form based on the "composition" idea (not defined by the database structure) he could pretty easily update it with this new field and add a bit of extra handling.