This might have been a good example fifteen years ago. These days with high-DPI displays you can't perceive a difference between font smoothing being turned on and off. On macOS for example font smoothing adds some faux bold to the fonts, and it's long been recommended to turn it off. See for example the influential article https://tonsky.me/blog/monitors/ which explains that font smoothing used to do subpixel antialiasing, but the whole feature was removed in 2018. It also explains that this checkbox doesn't even control regular grayscale antialiasing, and I'm guessing it's because downscaling a rendered @2x framebuffer down to the physical resolution inherently introduces antialiasing.