Several times I had the need to write mathematical formulas in my answers on CodeReview.SE. Sometimes, this can be simulated by
sub HTML tags, as I realized when syb0rg edited my answer here. However, sometimes it is not as easy, for example here, where I had to use code block for one formula (to achieve alignment) and LaTeX formulas off-site and attach them as images (for summations).
Formulas make sense in the design of various (for example, numerical) algorithms, as well as in the analysis of the algorithm's complexity.
My suggestion is to include MathJax in CodeReview.SE, as it was included in Math.SE (where it obviously makes even more sense to be included), unless there is some big drawback here that I'm failing to notice.