The biggest change though, was with regards to Facebook. WhatsApp says the update is “part of our plans to test ways for people to communicate with businesses [on Facebook] in the months ahead.” By coordinating with the Facebook platform, WhatsApp's maintainers will be able to track basic metrics about how often people use the services to tackle spam on WhatsApp. Additionally, Facebook will know your WhatsApp number and give you “better” friend suggestions and show you more relevant ads.
“We still do not allow third-party banner ads on WhatsApp. In the future, we will explore ways for you and businesses to communicate with each other using WhatsApp, such as through order, transaction, and appointment information, delivery and shipping notifications, product and service updates, and marketing. For example, you may receive flight status information for upcoming travel, a receipt for something you purchased or a notification when a delivery will be made. Messages you may receive containing marketing could include an offer for something that might interest you. We do not want you to have a spammy experience; as with all of your messages, you can manage these communications, and we will honor the choices you make.”
The WhatsApp blog post tried to assure users that their encrypted messages on the WhatsApp platform will stay private, even from Facebook. WhatsApp also promises that it won't share your number with others (except Facebook of course), including on Facebook, nor will they share or sell your phone number to advertisers.