Remove zero-width characters. Replace text on page with text of your choice. Replace swear/inappropriate words.
Cleanse warns you if you're on a page that contains zero-width characters and automatically removes them. Zero-width characters are invisible characters that are often used to identify you.
Cleanse also allows you to replace specified words on all websites with words of your choice. This is useful for parents to replace swear words or any other inappropriate words with something else. This can also be potentially used for pranks.