ATI 2019 saves to my.../AppData/Local folder
When I backup my Android phone to my chosen location, ATI 2019 also write lots of files to my .../AppData/Local folder. Why? And is it possible choose another location for them?
Not sure about the internal workings, but I suspect not. Appdata is a common location for user-profile specific tasks of an application that is available to all users of that computer OS. In your case, it may just be you, but in an environment where multiple users may be logging on, this is how applications make user specific changes.
As an example of how other applications also do this:
iTunes stores your iPAD/iPhone backups in C:\Users\xxxxxx\AppData\Roaming\Apple Computer\MobileSync\Backup
Google Chrome stores and modifies data for each user profile in C:\Users\xxxxxxx\AppData\Local\Google\Chrome\User Data\Default