On the GPU especially, having the data aligned to 16 bytes is huge just due to the nature of what a GPU is optimized for and the way memory access is designed.

On the GPU especially, having the data aligned to 16 bytes is huge just due to the nature of what a GPU is optimized for and the way memory access is designed. The speedup on x86_64 isn't as huge, but the aligned load instructions for SSE/AVX registers are still quite a bit faster than the unaligned load instructions. It can really add up when you're processing thousands of vectors every frame. The cache lines will only go so far when a single 3D affine transformation matrix (floatx4x4) already takes up an entire cache line by itself.