I used Texmacs all through my Master's degree. I loved it because it was excellent for quickly writing math, and building tables (I had to do this often). It would not have been excellent if I hadn't dedicated time to learning the keyboard shortcuts, but once I did, I could write math faster than writing it, and much faster than writing it in LaTeX. In timed take-home exams, I would just write the whole exam in texmacs because it was the fastest way for me to work.

To a lesser degree I also appreciated that the files have a similar feel to XML; I think it makes a lot of sense for this type of document.

I remember hearing about the macro system, but never looked into it. It sounded neat though.

When creating a technical document these days, I'd probably reach for typst though.