The way I see it, the main feature is being able to plug math formulas in, rather than formatting documents. It allows you to focus on your content (one feature of Markdown) while still being able to write mathematics.
In my experience LaTeX is quite poor at separating content from presentation, at least when you're unwilling to rely on the default styles. All the layout commands are context-sensitive, so I often end up writing presentation code in the middle of my content, or accidentally breaking the layout by moving content around.
