When one starts writing an answer, it is not possible to turn off the live preview of the answer. This makes it rather painful when composing long, latex-rich answers. The only way around it is to initially add an incomplete answer and then edit it—which then allows one to turn on and off the live preview.
This is silly---a bug in the design, really---and the initial answer box should prove the option of stopping the preview.
(Also, it would be better if instead of Hide the preview the button would stop the latex rerendering...)