Timelapse is the first thing that comes to mind. File size will be smaller. Another thing is when using the standard 24x16, the focus points stay mainly in the center. When using the 18x12, the focus points extend to the edges. I only use this feature if I feel like I need to put memory space in front of quality. If you are at an airshow and an hour in you've already used up half the memory card, pop it over to the smaller crop and more shots will fit on the card.The D7500 has the choice of image sizes, 24x16 is default with a choice of 18x12 (1.3) as the alternate. In what circumstances would you choose the latter?