If it’s something you use so infrequently why not have it on the screen in a toolbar instead, so you still don’t have to remember which key it is, and you don’t need to move your gaze away from what you were already looking at.

The touchbar has used, but from what I can tell, all those uses are better solved by existing non touchbar techniques already.

Toolbars for infrequently user functions you won’t remember the shortcut for (better because they hold more and don’t require you to change the screen you’re looking at, and you can keep your hands on the touchpad/mouse as before).

Fn keys (or combo keys) for frequently used shortcuts that you would remember as they ass tactile feedback and are much more conducive to touch typing.

The trackpad for actual scrubbing like functions.

Where I can see the touchbar being useful are infrequently used global functions, but I believe these are the ones Apple explicitly prevents developers from building (and unsurprisingly the inbuilt global ones from Apple are the most popular feature of the touchbar, such as volume controls and music playback controls).

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.