Discord doesn't reset formatting at the end of code blocks, leading to it bleeding over. For example, if you have a block of ANSI that has the background colour set by the end, then another later that only sets the foreground colour, it will keep the background colour from earlier. "Prevent format leak in" resets formatting at the start to prevent anything leaking into your message, "Prevent format leak out" resets formatting at the end to prevent anything leaking into other mesages. This does not affect how your message looks. If you don't think these will be helpful, you can turn them off to make your message up to 6 characters shorter.