How does auto CAD help in architecture?

The person above stated correctly, however, here's just another way of looking at the question... You can build an entire building start to finish utilizing AutoCAD, without having to buy a single nail... the 3D rendering that the program has can show you whether or not you should ever add a door here, or is the door opening the right way, or how much weight this wall is supporting, you can see all of that on AutoCAD, it's a very useful tool.