Webtrends Analytics 9 Adminstration Guide, November 2012
As a best practice, you should limit the number of children per profile to 20-25 child profiles. Large numbers of child profiles can cause performance problems.
Parent-child profiles have the following limitations:
Parent-child profiles are not supported in Analytics 10.
Child profiles cannot have server clusters, even if the Parent profile is configured to use them.
Because Visitor Data Mart does not store aggregated data in report-ready form, Parent-Child profiles are not available for Visitor Data Mart profiles.
Parent-Child profiles are not available for Webtrends Analytics 9 Small Business.