"By coordinating more with Facebook, we’ll be able to do things like track basic metrics about how often people use our services and better fight spam on WhatsApp. And by connecting your phone number with Facebook’s systems, Facebook can offer better friend suggestions and show you more relevant ads if you have an account with them."
WhatsApp ensures nothing its users share on the app, such as messages, photos, and account information, will be publicly made available on Facebook, but this still might not sit well with some users. Luckily existing WhatsApp users can opt out of sharing their data with Facebook for advertising reasons. Here's how: