You may see a warning message when using After Effects CC (12.1) that the GPU accelerated ray-traced 3D renderer does not have enough free memory to operate.
When the GPU acceleration of the ray-traced 3D renderer is disabled, the CPU version of the ray-traced 3D renderer will operate.
The message about the GPU-accelerated ray-traced 3D renderer not having enough free memory to operate is because of a change in After Effects CC (12.1) to actually warn you when your computer was in a dangerously low VRAM state. In After Effects CC (12.0) and After Effects CS6 (11.0), a computer with very little VRAM could still try to use the GPU accelerated ray-traced 3D renderer, but it would very, very, very often crash. So, now, After Effects CC (12.1) is just detecting the condition that would lead to a crash, telling you about it, and disabling the GPU acceleration until you have dealt with the problem.
So, how do you deal with this low-memory condition? You free up VRAM. This means closing all applicaitons that use GPU memory, which includes web browsers (yes, web browsers these days use the GPU). It also means disconnecting additional monitors, each of which uses a lot of VRAM. In some cases, restarting the computer is necessary.
This is primarily a problem on Mac OS with cards with 1GB of VRAM, such as the GT 650M in the MacBook Pro. These cards on this OS have just barely enough GPU memory (VRAM) to make use of the GPU-accelerated ray-traced 3D renderer under even the best of circumstances. If you want to use the GPU-accelerated ray-traced 3D renderer, you should really be using a more powerful GPU, one with more VRAM.
Note that this has nothing to do with the OpenGL GPU features in After Effects. Details of the GPU features are here: http://blogs.adobe.com/aftereffects/2012/05/gpu-cuda-opengl-features-i n-after-effects-cs6.html