Subject Areas in Oracle OBI are great for business users. They hide the complexity involved in warehousing projects and present an easy to use mechanism to create adhoc analysis based on the business user's need.
From an IT perspective, testing subject areas is fairly complex. Every Subject Area is really a grouping of Dimension Folders (with attributes) and Measures also known as Facts. The dimension folders may have 100s of attributes and connected to fact tables via foreign keys. Typically, this is referred to as the Star Schema in the industry. Engineers, Business Analysts, Quality Assurance teams struggle to ensure that business users do not encounter unpleasant surprises in the form SQL Errors when they try to create and execute analysis from the subject areas.