For reference, here's a tutorial on drawing a triangle in Apple's Metal, which follows some of the design principles as Vulkan, Mantle and DX12: http://www.raywenderlich.com/77488/ios-8-metal-tutorial-swif...

So, essentially, no validation, you have to manage your own buffers (with some help in DX12 I think), you can shoot yourself in the foot all day long. But if you manage to avoid that, you are able to reduce overhead and use multithreading.