Understanding Graphics Settings, low ,medium, high tier and Projects Settings>Player>Other Settings

So many options to configure for mobile. There are a few that I find puzzling. (this is for a Samsung Tab S2 Samsung Galaxy - The Official Samsung Galaxy Site)

1 Under graphics Settings, what determines whether Low, Medium, Or High Tier settings are used?

2 Under project Settings>Player>Other Settings there are a few that need clarification

-Multi threaded rendering, on or off?
-GPU skinning on or off?
-Device Filter, ARm FAT or x86?

I would also like to know what the tiers stand for.

As for the other, to the best of my knowledge:

Multithreaded rendering: Whether or not all rendering related CPU tasks are handled on the main thread or broken off to worker threads. If multithreading is supported by the hardware, turning this on will lighten the main CPU load for things like script execution etc. I think multithreading is automatically turned off on devices which do not support it.

GPU skinning: Again, support for this depends on the hardware and I think it’s automatically turned off on hardware which doesn’t support it. The idea is that when you have meshes which are skinned for animation (usually characters) the mesh needs to be transformed to match the position of the bones before it can be rendered. Some GPUs can do this transformation while other can’t. If the GPU can not handle the skinning, then the CPU needs to do the transformation before sending the mesh off to the GPU to be rendered. This means two things, the CPU now needs to do more work, and there’s an extra hit to your game’s performance as passing the data to the GPU every frame isn’t instantaneous.

And, finally, Device Filter: If I’m not mistaken, this allows you to specify which class of CPUs will be targeted by the compiler. In other words, you could make it so your game won’t run on any device which runs on x86 architecture.