What is the purpose of an AAE file? First, some background:

For those of you who edit photos using Apple software, you may have encountered AAE sidecar files, which are generated automatically by the Photos app (for iOS or macOS) when you export an edited image. These sidecars contain the data representing the edits made to the original image, such as crops or recoloring. Following an export, these AAE sidecar files will usually be located in the same directory as the original, exported image/JPEG file.

Theoretically, edits made to an image using the Photos app (on iOS or macOS) are "non-destructive," meaning that you can always revert to the original image anytime after editing.

Now, the problem:

For the life of me, I cannot understand if these AAE files are actually good for anything once they exist. If you try to import an original image file and its AAE into the Photos app, you only see the original image. The edits don't seem to transfer. 

Likewise, advice from Apple and user forums regarding the transfer of edited photos suggest that you use iMessage, AirDrop, or other methods to copy the edited image itself to the new destination. This process, however, defeats the idea of non-destructive edits since it will prevent you from ever reverting to the original image.

Finally, the question:

Does the AAE sidecar file serve any purpose? If so, what does it actually offer a user or program once it exists? Can we do anything with it?
According to several sources this feature was introduced with the launch of iOS 8 and OS X Yosemite (now macOS Yosemite).

The AAE file format is proprietary, which usually means that only Apple, and Apple-approved, software can interpret the contents. Some cross platform apps that can take advantage of the AAE format are Lightroom and Photoshop. However the file appears to be a regular XML file.

A sample file for a slow motion video would look like this: https://pastebin.com/raw/1r8416rm

The data tag is encoded with base64 and, when decoded, contains a property list (.plist) formatted file that looks like this: https://i.imgur.com/CYPVcTO.jpg

Simply put, an AAE file contains information that specific apps can use to apply effects to photos and videos based on edits that a user makes in the iOS Photos app.