The Selected Member data display option specifies that the query result set should include the member from which advanced member selections are defined.
For example: If you specify Also Select Children on the Year dimension member and Selected Member is enabled, Year and all of its children are returned by the query. When Selected Member is disabled, only the children of year are returned.
This Selected Member functionality also impacts the drilling result set, by including or excluding the drilled member in the drilling result set.
Additionally, you can enable the Selected Member First data display option, to ensure that the drilled member is listed above the drilling result set.