Calculated collections uses

Chapter 4 Managing Profiles

You create calculated collections to:

Display user-defined dependencies for a selected object, the calculated collection is displayed in the Dependencies tab of the object property sheet. You can double-click items and navigate among user-defined dependencies
Fine-tune impact analysis by creating your own calculated collections in order to be able to better evaluate the impact of a change. For example, in a model where columns and domains can diverge, you can create a calculated collection on the domain metaclass that lists all the columns that use the domain and have identical data type
Improve your reports. You can drag and drop any book under any other report book and modify its default collection in order to document a specific aspect of the model

For more information on calculated collections in the report, see the "Modifying the collection of a node" section in the "Building reports" chapter in the Reports User's Guide .
Improve GTL generation since you can loop on user-defined calculated collections