You can bold and italicize to your heart’s content when you write a letter to your grandmother. That’s okay. When you write a document of any decent size, say bigger than three pages, you must use styles. Here’s why.
Why you need to use styles
The last unit study I wrote has 5,687 words in 70 pages. It has eight level 1 headings and 47 level 2 headings. I didn’t count the level 3 headings. The document has a bunch of links in it, tables, and pictures. Each picture has captions under it. There are a few quotes in the document. Now, let’s say after I wrote it, I need to change the color of the level 2 headings. Forty-seven changes are required. Maybe the URLs need to be in a special font with a unique color, and that requires another ridiculous amount of changes.