if you are in a small room where you would only need 2x AA to antialias the whole scene, then that is actually a very good idea because it would boost preformance without any loss in image quality, If you want to talk about cutting corners, then let's have a talk about Nvidia's anisotropic filtering. They cut some major corners on it, if you leave image quality at the default setting of "quality" in the nvidia drivers, you will notice a lot of texture shimmering with AF, and when you set image quality to higjh quality, the shimmering goes away, but at the cost of 10-30 fps depending on what game you are playing and what you are looking at.