Ok. Here is the thing. I was using my PC for a while this way. Then I said this to a guy in a computer shop. He said that this is not good for my motherboard and it will consume half of my motherboard life. Is this true? Coz I don't see anything like that. Normal heatings and everything runs normally. The reason I use iGPU is when I plugged both monitors to the same VGA it lowers my gaming performance. Hope to find some answers.
No, using onboard and discrete at the same time won't affect the lifespan of your motherboard. I guess his reasoning is if you're drawing in power for both, that means 2x the power, 2x the heat, 2x faster motherboard dying. But it doesn't work anything like that, and won't physically damage anything.