Google owns the top visited websites including the search engine (Google.com) as well as the YouTube. It servers billions of visitors daily with billions of activities especially for YouTube. Every single second, data is transferred from one to another and without powerful data management; it will be a big mass which will result in slow process. Google has many data centers across the world to make sure that data can be transferred faster in each region.
To see how it works, you can watch the video above.