This application is a hold over from "Architectural Desktop". Before Revit, this was a quasi attempt to turn AutoCAD into a Building Information Modeling application (BIM). AutoCAD Architecture is what is left standing of that product.
When it first came out it was powerful. It was a 3D modeler made for architects. Standalone AutoCAD always felt like software meant more so for engineers. This made it more for architects. Which was great.
You could now created 3D Walls, and doors, and windows. Model your design in 3D with real architectural elements rather then just lines, circles and arcs.
This is a very outdated application. Autodesk (the software manufarcturer) has put it's efforts into developing Revit, which is it's main BIM offering. AutoCAD Architecture has become obsolete.
We have it on the floor at the firm I work for, however we do not use it as a 3D modeler. We only use the 2D autocad workflows. If we are goign to model in 3D we will use other applications such as Revit, Rhino, Sketchup, etc.
I do not recommend. For architecture 3D Modeling, go with Revit.
We use 2D AutoCAD on several projects for documentation. Howver, we do not have any projects using full AutoCAD Architecture.