Yes, using the keystone correction reduces the resolution of your projector resolution. When you use the keystone correction for the projector projection alignment. Because keystone correction direct changes your projector resolution. It's not necessary you will something a big difference in the image. It depends from person to person. And how much you have done the changes. If your projector screen is doesn't have black order. You may see the grey box on your screen. Which is visible around the image. And also you may feel some lag during gaming. That's why it is bad for the projector image alignment.