The new iOS 11 Notes app is already far better than the previous version, but this one new feature might tip you over the edge. Now you can draw on pictures with your Apple Pencil, just by tapping on them.
Previously, images and sketches lived side by side, but could never meet. Now, with the power to scrawl directly onto images, you can do all kinds of things. Example: I keep a blank sheet of guitar tab notation paper in the Files app, then drag it to a note and start writing on top of my template. That’s just one use. Another might be to draw mustaches on pictures of your workmates.