What does IGPU Multi-Monitor do?

From page 68 of the manual:

IGPU Multi-Monitor
Select disable to disable the integrated graphics when an external graphics card is installed. Select enable to keep the integrated graphics enabled at all times.

I’m pretty sure it’s just a misleading name. My experience is that with Multi-Monitor turned off, you won’t get video signals from the iGPU at all while the dedicated graphics are active.