About memoir and titlesec incompatibility

Question

In page 2 of the titlesec documentation, Javier Bezos writes

titlesec works with the standard classes and with many others, including the AMS ones, and it runs smoothly with hyperref. Unfortunately, it is not compatible with memoir, which provides its own tools with a limited subset of the features available in titlesec.

I don't use the memoir document class so I am not familiar with its features, but I've made a few simple tests (really few and simple) using it together with titlesec and couldn't detect any problems. To what extent can titlesec be safely used with memoir? Which exactly are the incompatibilities mentioned?

Answer 1

For chapters the incompatibility is not evident, as \titleformat{\chapter}... will redefine \@makechapterhead and \@makeschapterhead. However

\documentclass{memoir}
\usepackage{titlesec}

will redefine \section in such a way that the second optional argument is not accepted; indeed

\section[section toc][section head]{section title}

will produce the correct entry in the table of contents, but

1.1 [
section header]section title

in the document in contrast to what memoir's documentation advertises.