Basic formatting - Bold, Italic and Underline
It can be very useful to emphasize text through various types of formatting. Formatting changes the fundamental appearance of text and will draw attention to itself, especially when placed in conjunction with normal text. In many documents you can use it whenever you like, although there are definitely circumstances where it is more appropriate.
For instance, if you are writing a marketing document, you may want to place some words in bold or even underline them to make them stand out and become more appealing to your readers, such as brand or product names. Select only the words that will make the biggest impact, that you want to highlight for your audience.
In some academic articles, or simply to assist your readers, you can italicize or underline the names of books, movies, or TV shows, as well as citations and references.
Headings and separators can also be bolded to make them stand out against the unbolded text of your main article and direct readers to different sections quickly.
While formatting can be a healthy addition to a document, be sure not to overuse them!