Most developer tools (which is the context that comes to mind for me) have some sort of quick lookup for unfamiliar functions (eg. Sublime Text's command palette, IntelliJ 'find action by name' etc etc). These facilities don't require you to look away from the screen, and give access to far more commands than the touch bar. Anything used often enough to be worth mapping you can remember within a day or so of use, so it seems like a tiny gain for losing one whole row of touch-typeable keys.