Sometimes it is more convenient to write a formula (or non-formula LaTeX) on more than one line. For example, I recently wanted to write
!math f(x) =
\begin{cases}
e^x, x \in \mathbb{R} \\
0, x = -\infty \\
+\infty, x = +\infty
\end{cases}
However, to get Fletcher to parse it correctly, I instead needed to put it all on one line, as !math f(x) = \begin{cases} e^x, x \in \mathbb{R} \\ 0, x = -\infty \\ +\infty, x = +\infty \end{cases}, which is even less readable than LaTeX usually is.
Done.