Comment by aharrison

Assuming your question is in good faith, the answer is: when you rent something on AWS, you are paying for total cost of ownership sliced out. When you run something on your gaming rig GPU, you already paid for the machine/GPU - now you are "just" paying for electricity and depreciation. So if you have a gaming rig sitting around while you are writing a web app or whatever, let it do some science for just the cost of electricity.