What does the central-identity model mean for the user: benefits and problems?

The user only has to maintain one or a few identities and can use them at many relying parties, but the identity provider is involved in every login and can profile when and how often the user visits which RP; the user must fully trust the IdP and becomes dependent on it.

Benefit: fewer accounts, fewer passwords, single sign-on across applications.

Problems:

• Privacy: since the IdP performs the login function for every RP, it can remember every visit. Such profiles feed targeted advertising and, in the wrong hands, surveillance.
• Trust: the user must trust the IdP completely with their data and their access to everything behind it.
• Dependency: if the IdP suspends the account or goes offline, the user loses access to all the RPs at once. A person locked out of a major platform account can discover how many services they had linked to it.