The people using it will probably have an easier time navigating Unicode text than they would have if they had used other existing libraries or tried to roll their own.
It's more a comment on the users who need to be warned that "no, you probably don't want your C program to know if that string actually fits in the 80 column terminal".
There is an MJB_FEATURE_CHARACTER_NAMES option you can set to zero if you don't want to have a function that returns the name of a codepoint, such as "LATIN SMALL LETTER E WITH ACUTE". This is something that probably most people do not need at all. This shrinks "Hello World" macOS ARM executable from 937KB to 663KB.
I should probably offer other runtime options so users can literally strip away everything they don't need. For example, as you suggested, measuring whether a string is less than 80 columns is something you don't do every day.