A CrossPlatformBuild record must have at least one SCLMBuild or CCBuild child record associated with it, but it can have more. Before you create a CrossPlatformBuild record, you need at least one SCLMBuildConfig or CCBuildConfig configuration record to use with the SCLMBuild or CCBuild records you create.
For example, if your group hierarchy contains the groups DEV1, TEST, and RELEASE, you could enter "DEV1, TEST" into this field to track build and promote operations on an SCLM artifact to the top of the project hierarchy.