Currently it suggests to switch to the discrete graphics card (an ATI card in my case), if an external monitor is detected non boot. If no external monitor is detected, it suggests to discable the discrete card, to save power. And because hybrid setups just appear in laptops, it usually makes sense to save some watts.
During the last weeks I've learned that it is not possible, to determin if a monitor is connected, when the discrete card is disabled. If I wanted to detect a hot-plugged monitor, I would need to do some polling (including turning the discrete card on and off), but this didn't seem to be to good, so I skipped it and just provided the basic functionality described above.