Adobe's Business Catalyst can be a great CMS, but it does have it's limitations. It can be a perfect system for many clients. Some web developers will be frustrated by the lack of backend control and the slow feature innovation with the system. One very useful tool within Adobe BC is the content holder modules, which can act like editable include files for templates.
Some web designers would like to use content holders in more complex ways using layering. You can place a content holder module within another creating recyclable components. These components can then be integrated within a larger, encapsulating structure using another content holder.
There is a limitation however. The Adobe BC system can only allow for this layering to go three levels deep after the first module. The fourth recursive module will not render.