If you’re giving a presentation, for example, and you want to use animations and transitions so don’t want to write it entirely in LaTeX. You may want to still use LaTeX to get well-formatted equations in your presentation. These need to be included as pictures as most presentation programs don’t natively support LaTeX.
This guide will tell you how to use LaTeX to create standalone pictures of equations for use in anything, from presentations to websites. Update: I have now written a bash script to do the same as this, but easier to use and better, explanation in this blog post.