Every time you want to hand a picture you have to take into consideration all the other pictures already on the wall. It’s hard to move them because they are hanging in a fixed place on some hook. When you find a place for the new picture, it becomes even more difficult the next one.
Have a layer beneath the wall’s final finished layer that has metal disks spread in a matrix all over the surface of the wall. Each time you want to hang a picture, stick a few strong magnets to the back of the frame and just let the magnets attach to the wall anywhere the underlying metal disks are. You can move the picture quickly any time to any new location without and trace of where it was (like a hook or a nail sticking out), or even rearrange all of the pictures on the wall if you feel like it.