Class types [Types of classes]:
The selection under Class types [Types of classes] determines which options are available on the Classification dialog page in the list box under Filter.
Instance types [Types of instances]: Classes / Attachment points [Connection points] / Classes and attachment points [Classes and connection points]
The selection under Instance types [Types of instances] determines whether the Instance column on the Classification dialog page is editable or greyed out.
Example: In the plant manufacturing the use of instances would possibly make sense for pipe connections.