In order to optimize an article marketers will try a number of different SEO optimized headlines to see which one brings the most viewers in. They might find that different headlines work well for different areas of the internet or for different target markets.
Metrics can be gauged relating to how many click throughs each article gets, the amount of social media sharing and the level of user engagement. The variations that do not test well will be taken down and replaced with ones that have higher metrics.
It is also used as a way to link the same article into a number of different aspects, if the article relates to more than one subject it may have headlines that identify with one subject and a new set of headlines that identify with the other.