When I write a post in WordPress, I always push the “Save Draft” button in between. WordPress then stores the article in the database as a separate revision. So each time I save my draft, a new record is added to the database.
The revisions for a small article like this are stored in several records in my WordPress database. Altough only one of them is published. This mechanism gives you some kind of versioning of your articles, but it also produces a lot of overhead in the database, because the records remain in the database and “inflate” it unnecessarily.
Fortunately, you can configure how WordPress handles the revisions. It is possible to completely disable revisions, or limit to a maximum amount of revisions per post.