Here's a really generalized breakdown:
The VRAM of the GPU is used to store information that the GPU needs fast access to. In games, this would be textures and geometry. In CAD and other 3D applications it also stores similar data.
In games and CAD, the only performance increase would be due to the fact that the graphics card would be able to load more/larger textures & geometry.
The issue here is that the 330m is not a high performance graphics card. It is too slow to render high detail textures and geometry that are capable of being stored in 512mb of VRAM.
In other words, you will see very minimal increases with the bump in VRAM.
Also, to those wishing for 1gb of VRAM: unfortunately, 512mb is the hardware limit of Apple's design, they technically can't have any more than 512mb due to the chip setup that they use.