KaTeX does not support LaTeX commands like \label, \eqref, \notag, etc. As long as one does not need them, KaTeX is good. But if one needs them, MathJax becomes

KaTeX does not support LaTeX commands like \label, \eqref, \notag, etc. As long as one does not need them, KaTeX is good. But if one needs them, MathJax becomes necessary. I often do need these commands, especially while writing proofs, solutions, or long mathematical posts. See https://susam.net/blog/integrating-factor.html https://susam.net/blog/integrating-factor.html for an example. These commands make it convenient to refer to previous results using equation labels and numbers in long articles. One can work around the missing support for these commands in KaTeX by writing their own HTML to simulate the same functionality but it is nice to have MathJax do this for us automatically.