The benefits of using Facebook's conversion tracking is because if your objective is to get people to sign up or buy products on your website. You will be able to track which specific demographics, age groups, and ads particularly are the ones getting you the most sales.
Not only that...
But more importantly after about 30 conversions of solid data, Facebook will get smart, and show your ads to people who are most likely to convert on your page. This is done over time Facebook gathers the data history of the potential people who convert already on your website and combine that to lookalikes or users who have the same interests, and behaviors.