OK- Look at people trying to make 3D games for the web. GPU performance is a concern, but if you can't even run the physics simulation or cull your object database fast enough to push triangles to the GPU, your performance will be hurt and the GPU will be idle. People want games based on WebGL to have comparable performance to native apps -- well, you're going to need to take all of the libraries that games use and convert them too. This is a good solution to allow such SIMD optimization that have been present in native libs for years to have a chance to surface in JS libraries.