Avoid visible attribute hierarchies for attributes used as levels in user-defined hierarchies
This rule analyzes each database dimension to determine whether attributes that are used as levels in user hierarchies are also visible as attribute hierarchies.
To increase usability, you should typically hide attribute hierarchies that are also used as levels in user hierarchies. Users might become confused if attribute members are visible in different ways. To hide an attribute hierarchy, change its AttributeHierarchyVisible property to False.
An attribute usually does not need to be exposed in its own single-level hierarchy when that attribute is also included in a user-defined hierarchy. This duplication only complicates the end-user experience, without providing additional value. You should consider renaming either the level in the user hierarchy or the attribute hierarchy.
One common case where it is appropriate to present two views of an attribute is in time dimensions. The ability to browse by [Month] and the ability to browse by [Month-Quarter-Year] are both valuable. However, these two month attributes are actually separate attributes. The first contains only the month value such as “January,” whereas the second contains the month and the year such as “January 1998”.
For more information about how to hide and disable attribute hierarchies, see Hiding and Disabling Attribute Hierarchies in SQL Server Books Online, and see the section, "Using hierarchies effectively," in the SQL Server 2005 Analysis Services Performance Guide.