After Effects CS6 does a better job of harnessing OpenGL and the video card in your computer when drawing images to the screen. This results in faster interactivity, a more highly responsive work environment, and a smoother user experience.
You get improved playback of memory-cached frames as well as improved performance while working in larger Composition, Layer, and Footage viewer sizes (particularly useful for working with larger image formats and on larger displays). Specific benefits include faster manipulation of layers with graphical overlays such as bounding box handles, masks, motion tracker points, and motion paths, as well as working more efficiently with viewers that contain overlays such as guides and grids, custom user interfaces for effects, and interactions like brush size adjustments.
Based on early tests of After Effects CS6 performed by NVIDIA, depending on hardware configuration, many of these functions have been accelerated by a factor of 1.5 to 2.5 — with some (such as grids, guides, and rulers) as much as 16 times faster than before.