Linkedin is worse than Facebook in terms of privacy. So many dark patterns on their site - someday their reckoning will come just as facebooks. Easier target too since it could hurt people’s jobs and careers.
Based on users' data and behavior, one can anticipate whether or not he/she is going to quit/leave his/her current job. Microsoft recruiters can then swoop in and offer him/her a job.
Or for example, Microsoft can essentially map all the top IT talents network and use this to its advantage.
The list goes on...
The real advantage would be to map everyone and every company to get intelligence on the users and potential users of their products (Office 365)
And that sucks since it's hard to have a professional life w/o one. I've known women who were stalked/harassed because despite otherwise being pretty locked down their harassers found their linkedin and used that to harangue them.