The battle for the post-cookie advertising identity model is heating up, with Apple, Facebook, and Google all playing to win; see Measuring Conversions on Facebook, Across Devices and in Mobile Apps (Facebook for Business blog) for more details
"With the new cross-device service announced Wednesday, Facebook is aiming to prove that mobile ads can lead to purchases, even if those purchases are not necessarily made on a smartphone. In a study with Altimeter Group, Facebook found that among people who showed interest in a mobile ad, more than 32 percent took action on desktop computers within 28 days.Facebook to track users across devices to study shopping habits - Business - The Boston Globe
Because Facebook’s users must log in to use the service, the company can link their identities with their behavior as they switch among devices throughout the day. That allows Facebook to give more information to marketers than they could glean from other online tracking methods, such as cookies that log activity within a Web browser."