XBox Controller Question - What does Left DPad do?

So I'm trying to use a gamepad and selected XBox controller under options. I think I've figured out all the XBox controls except the Left DPad. For example, Right DPad + X, Y, B or A is Device 1-4, Down DPad + X, Y, B or A is Builds F5-F6

I cannot figure out Left DPad at all. Could anyone shed some light? Thanks!