I think they have connections/lawyers that could help sue for civil rights violations.

Also, if the police are doing something sketchy to one person, then it is probably not the only instance, and an organization like the LDF could pursue the broader issue.

By analogy, if a corporation steals $20 from you, it may not be worth personally crusading for it back, but if you tell the right person about it, they might file a class action.

If you are a person who has been recently persecuted by the police and have a fear of police overaction contacting the LDF to help you navigate interacting with the police in any manner seems completely legitimate.