Here’s a screen shot of Page 1 and Page 2. They are perfectly aligned because I used snapping to make them perfectly aligned.
Here’s what happens when I move Page 2:
Notice the background object from page 1 gets dragged along with page 2 because it happens to be “touching” page 2.
Let’s say I’m working with page sizes that are 1920x1080px
1920x1180px
1920x1080
Perfectly aligned with a perfect 100px
gap: