Mainstream news and corporate social media are omitting more and more information about the world that doesn't benefit their aims. With a keystroke they can kill important news that might incite people to act, while pushing news and ideas that will pacify and normalize what is effectively dystopia.
There are many places in the world where it's difficult to find likeminded folk, such as deeply rural areas in red states. Seeing that there are others out there can be a huge mental relief, and may even help them connect with others to enact direct action with.

Federated Social Media by its nature cannot be controlled for the sake of corporate interests, which is unfortunately a rare trait at this point in time. What this can effectively become is a new Citizen Controlled Media, as described by Noam Chomsky. This will become essential to spreading news of real events and ideas on how to resist while bypassing the corporate filter.