Crop, mask, or erase parts of content and photos
Just a few examples: I would definitely want to apply, for instance, a paper texture behind (or into) a frame. If the frame is hand-drawn I may want to create a mask that follows the contours of the frame. Or if the frame and texture are of different proportions I may want to crop the texture so it fits. Or I may not want to scale the texture down, so I would create a mask to reveal a portion of the texture at 100% of size.
Being able to not just make your photo big or small, but to change it from a rectangle to a square or vice verse. Same with the frames. That way it’s easier to fit a frame over a photo.
Ripping would show an irregular edge with a contrast color, just like paper that has a coloured core.
Nicole on 1/9/20: Erase around photo for custom shape. Masking / clipping path tool
Cutting tools ("Paper Edgers", "Pinking Shears", etc.). People use these to shape items that they add to their pages, from washi tape modification to "collage-style" cutouts.
Photo cropping as rectangle and freeform
To mask objects (e.g. pull a travel stamp of your passport while removing the background). This could all live in the in app camera (if there is one).