What does IGPU Multi-Monitor do?

I recently put together a new computer and was interested in the idea of using the integrated graphics to possibly take some of the load off of the graphics card by managing my second screen; or something like that.

• Intel Core i3-4150 3.5GHz Dual-Core Processor
• ASRock H97M PRO4 Micro ATX LGA1150 Motherboard
• Gigabyte Radeon R9 270X 2GB WINDFORCE Video Card

I was looking around in the BIOS, and first noticed that there was no setting to turn on both the PCIe graphics card, and the onboard integrated one. But there is a setting labeled "IGPU Multi-Monitor" and I am not sure what this does. There is no real description for what this setting is for. Based on its name, it could just be a setting to enable two monitors to run off of the IGPU alone.

What does the setting IGPU Multi-Monitor do? What are its benefits/downsides?

Main idea is that, while you are using your dedicated GPU, you can still use video-ports on your motherboard. So if your Radeon or GeForce does not have say VGA, but your motherboard has, then you can connect your monitor to it. In this case your main GPU will continue to render games and video, but will send image for VGA monitor to Intel GPU.

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.