Form construction is quite expensive (specifications, FormFactory, blablabla), so you don't want to instantiate useless forms, that would make some overhead.

* Sometimes we want a specific forms for `addAction` and `editAction`, so you don't want to instantiate `CreateUserForm` when the request will be dispatched to `editAction`

* If the request is going to `deleteAction` you don't want to instantiate the form.