If you look at the help for this feature, you will see that the transform is required when the class name of the save-to differs from the class of the data page.  Here is what it says:    

If you selected Database save,

1. In the Class name field, enter or select the class whose data you want to persist.
2. If the class in the Class name field is different than the class of the data page, in the Data Transform field, click the rule opener icon to create a Data Transform using a template. This data transform maps the data page class to the Class name field.
3. Optional: In the Validate rule field, enter or select a validate rule.