So recently WhatsApps and Facebook announced that Facebook would start using your WhatsApp data to deliver targeted add's to you on Facebook, if you are as unhappy about this as I am the good news is you can opt out of those terms and conditions, although you need to do it quickly to prevent data from being sent over to Facebook from WhatsApp.
Theres appears to be two means of opting out - at the point your asked to accept the terms, and one retrospectively
The first method unfortunately can only be done if you haven’t accepted the new terms, using the pop-up that will emerge when you open up WhatsApp. If you haven’t, wait until that happens but don’t click “agree” – instead navigate to the smaller “read more” option, and unselect the box that says “Share my WhatsApp account information with Facebook”.
If you like many people just accepted those new terms, you can still opt out – as long as it’s within 30 days. You just go to settings menu in the app, and pressing on the account tab – there you’ll find a “share my account info” button that you can undress and revoke your permission.
WhatsApp say that the new change is meant only to help improve the ads on Facebook, so the only possible consequence is that what you see on the network might be slightly less relevant.
This is what they have said on the matter:
But 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. For example, you might see an ad from a company you already work with, rather than one from someone you've never heard of. You can learn more, including how to control the use of your data, here. - https://blog.whatsapp.com/10000627/Looking-ahead-for-WhatsApp
However when you look into more detail they also said:
Nothing you share on WhatsApp, including your messages, photos, and account information, will be shared onto Facebook or any of the Facebook family of apps for others to see. This means, for example, although some information will be shared with Facebook (such as your phone number), that information will not be seen by other people on Facebook. In addition, when you and your contacts use the latest version of our app, your messages are end-to-end encrypted by default. When your messages are end-to-end encrypted, only the people you are messaging with can read them – not WhatsApp, Facebook, or anyone else. - https://www.whatsapp.com/faq/general/28030012