Company Umbrella’s? Shells? What?

I recently heard Richard Branson’s Virgin Group is a parent company to 199 other companies like Virgin Mobile, and Virgin Coke, etc. My ? is: what is the benefit of this? Where can I find in depth info into this structuring process and why would a company do this. I heard other companies do this as well. How do you know which ones structure like this? Answers to this question seem very murky and hard to find.