1. You can easily implement your own window manager in it, e.g., replaces Moom or Magnet.
2. You can bind any AppleScript, shell script, etc... to a keyboard shortcut.
3. You can record and replay GUI macros, e.g., like Vim and Emacs macros but for any application.
4. At has a ton of built-in actions to script practically anything about your system, e.g., sleep, simulating media keys, image manipulation, etc... I suspect a lot of uses of Karabiner can be replaced by Keyboard Maestro.
5. It has a built-in clipboard history, with powerful features, like, processing an item from the clipboard with a Keyboard Maestro macro. One I use sometimes is running OCR on a screenshot I have on the clipboard.
6. You can bind any menu item in any application to a keystroke. E.g., you can rebind menu items to other keys, or adding key bindings to menu items that don't have keyboard shortcuts.
7. You can create custom command palettes (i.e., like ⇧⌘P in VS Code) for applications. For example, the command palette in Photoshop is awful, so I just made one for my common actions in Keyboard Maestro instead.
All of the above can sync seamlessly between computers with any file sync service (e.g., Dropbox). It's probably the best sync I've ever used, in 5+ years of use I've never had even the slightest hiccup. I don't bother using macOS built-in settings for things Keyboard Maestro supports for this reason. Put it in Keyboard Maestro and it will automatically sync to any Mac I use (I always install Keyboard Maestro).