One widespread method for stealing content is blog content scraping. This is where content is taken from your site, usually via your RSS feed, and republished on another site.
Sometimes your content will be simply copied and pasted directly to another website, including your formatting, images, videos, and more.
Other times, your content will be reposted with attribution and a link back to your website, but without your permission. Although this can help your SEO, you may want to keep your original content hosted on your site only.
Usually, the main motivation for content theft is to profit from your hard work.