The disadvantages of formal channels are that organisations have a large advantage in resources, there are long delays and only narrow aspects of the case are dealt with. Several Australian governments have introduced or are considering legislation to protect whistleblowers from reprisals. This sounds like an excellent idea, but it has severe limitations. The legislation can only cover certain types of individuals, typically public servants, and particular types of dissent. But many types of problems are hard to legislate against, such as subtle harassment campaigns and blocking of appointments.
Legislation has potent symbolic value.
On the one hand, it may legitimate dissent. On the other hand, it may give the appearance that something is being done about suppression when actually little has changed. When unions or staff associations take up defence of a dissident, this can be very effective. Publicity is undoubtedly an extremely potent method of opposing suppression. Furthermore, journalists often are interested in suppression cases because they make a good story.