πŸ”– Federation is the Worst of all Worlds (archive)

The threat model and economics of federated systems devolve to concentrating trust in the hands of a few, while missing out on the scale advantages of purely centralized solutions.

Since privacy isn’t always built into the protocol the user has to trust the federated server. The problem can be partly solved by building a privacy preserving data persistence layer, and an application layer on top of it.