Reveal codes seem, to me, to be "show invisibles" but for the markup such as font changes and such? The first search results are all of the "they're gone, what do we do?" And seem to assume you know what it is already. I don't know what I'd use it for other than me being OCD and I'd probably just ask myself "why am I not using TeX?". Care to explain what you've found so useful about it?