Rob has it right, I know what this line is supposed to do but every other time I use it by arranging/tiling some new images, it just moves almost over to the right where I have all my icons.... Then I have to move an image to find the orange line again, move it life then resize and they image go to the right spot.
This is a brand new workspace where I just loaded 3 new images and while cropping them the orange line moved to the right all by itself. Now if I tile the images, they overlap my icons.
Sorry but this is just a distraction and a minor but irritating PITA.
This is a standard Dell official 4K monitor and it does the same on another 4K TV monitor, so it is not the display.