When you edit a page, you can use the Preview button (located right next to the Save page button) to see in advance what your edits will look like. This lets you check your work periodically without filling up the page history by making lots of smaller edits. The preview function can also help you avoid mistakes, such as when using an unfamiliar type of wiki markup. The preview will appear together with the edit box you have been working in (either above or below it, however you prefer).
An even faster way to preview a page is with the keyboard shortcut ⇧ Shift+alt+P.