The advantage to this is total control over your HTML documents. You are not limited to the capabilities of a specific web development tool. The disadvantage is that you personally must know how to type HTML commands. There is a greater chance of causing problems such as typos when entering everything by hand. Also, you don't get to see what the page will look like until you load the page into a web browser.
People often find that they use other web development tools to build the web site.
However, they still need to resort to hand tweeking with a text editor to get around limitations of their development tool. Some text editors have HTML extensions designed to make it easier to develop web pages. They often include syntax checking, checks for standards adherance, spelling checkers, and other advanced features to assist the HTML developer. These editors are designed for maintaining individual web pages, but do not include features for maintaining an overall web site. Also, the editors often do not really show you exactly what you would see in the web browsers.