What is MTL Compiler Service

This question was never answered, and I came across the answer from a Quora user:

MTL Compiler Service, better listed as MTLCompilerService, is a compiler for metal shaders, that can pass information directly to the GPU. It was released in iOS 8 as an alternative to using OpenGL. There’s a variety of performance reasons for the switch, though Apple fully supports use of both currently (with Metal being their preferred route).

Basically it’s what runs between your application and your GPU/Video Card to speed up graphics processing and makes things prettier.