Don’t worry—your messages, photos and other media shared through WhatsApp won’t be automatically posted on Facebook for others to see.
“We won’t post or share your WhatsApp number with others, including on Facebook, and we still won’t sell, share, or give your phone number to advertisers,” reads the post.
Again, only account data is shared with Facebook, not your chats and media.
Data sharing is purely for the purpose of improving users’ Facebook ads and products experiences, the company ensures. It also lets it do things like track basic metrics about how often people use these services and better fight spam on WhatsApp.
After accepting data sharing, you’ll see better friend suggestions and more relevant ads on Facebook. “For example, you might see an ad from a company you already work with, rather than one from someone you’ve never heard of,” says the firm.
More information is available in this WhatsApp support document.