For any predefined schematic builder provided with this version, there is an option on the schematic builder properties page called Automatically create schematic feature classes. When this option is checked on the properties page, the content of the schematic diagrams implemented by the diagram template is not fixed at all; on the contrary, it is very opened. If the context set by users when they ask for diagram generation is understandable for the schematic builder (for example, a set of features coming from any geometric network currently selected in a map document will be always understandable for a Standard builder, while it will be not understandable for a Network dataset builder), the builder is able to analyze the context in input, create the appropriate schematic feature classes in the schematic dataset (if they don't already exist), populate them by creating the appropriate schematic features regarding the specified context, and generate a diagram.
Using the Automatically create schematic feature classes option may be useful when you are in the very first steps of your schematic dataset configuration or when you want to quickly generate schematic diagrams for first tests with a minimal amount of setup work, but it is strongly inadvisable to keep this option checked in an advanced phase of your schematic dataset configuration. Conceptually, a schematic diagram template is created to generate a particular type of schematic diagrams containing a set of expected types of schematic features. If you specify a schematic diagram template based on the Standard builder, for example, while the Automatically create schematic feature classes option is checked, the Standard builder will be able to deal with any geometric network, and the schematic diagrams implemented by this diagram template may be not very consistent.