For me, I think it's a novel concept, but it's rarely used in practice. I like having it as a scrub bar for video/audio apps or for fine-tuned volume control and it's nice for emojis. But other than that, I rarely interact with it.
The ironic thing is that I would use it a lot, if, and only if, there were any browser which displays tabs as favicons on the touch bar.
But there just... isn't. It's completely baffling, the Safari preview is useless and Firefox has a 'touch to select address bar' button which I always forget is there.
But I also wouldn't be particularly sad if it disappeared.