If someone is editing a page and presses cancel inadvertently, wiki will take that input and will leave the editing page without giving the user any sort of notice that the work will get lost. In contrast, pressing the back button on the browser prompts the user whether he/she wants to really leave the page. In many occasions people in my team have lost their work by pressing cancel inadvertently. Matters get worse as the save and cancel button are so close to each other.