My thought about the touch bar is that it starts to tackle a problem which began in the 1990s once desktop displays hit 1024x768 pixel resolution and has only gotten worse as displays pushed to larger and larger size.
Namely: the display was originally small and easy to mouse all the way across, meaning the menu bar and toolbars were always in close reach, and moving the mouse from the current position to the menu bar and back was fast and precise and not too disruptive to work with the pointer.
As displays grow, the menu bar, toolbars, and other on-screen non-content UI controls keep getting further away and more disruptive to reach for with the cursor. If you frequently need to precisely mouse across a 30 inch display, click a button, then precisely mouse back to where you started to carry on with a content creation/editing task, you’ll start to hate performing that action and look for ways to avoid it. But often there are actions which can’t be handled by keyboard shortcuts, or software with so many functions that remembering the keyboard shortcuts is a chore.
The original justification for a fixed-position menu bar at the edge of the screen was that by Fitt’s Law, it would be very predictable, efficient, and cognitively easy to navigate menu options. As software gets more complex and displays get bigger, that justification starts to break down.
The touch bar is a way to restore the fixed-position nature of the original menu bar and even improve on it, moving tools off the virtual screen and into the physical space of easy-to-reach direct finger touches, letting someone drive a contextual toolbar while hardly moving their fingers off the main section of the keyboard.
I haven’t seen anyone else try to seriously tackle this problem on a desktop/notebook. Certain niche software has adopted gesture interfaces or radial menus, tried to cover every possible command with keyboard shortcuts, or adopted something like the Quicksilver/etc. command-line-with-text-completion UI, but usually the usability of all of those for non-experts has been poor.