While not directly leaked documents, documents from FOI requests are similarly good at accessing ground truths.
I've given a rough first answer with some things that made me update my model of the world to think that spies are powerful and coordinated enough to keep secrets, but not competent enough to keep them forever.
Some specific learnings:
It's important to read these in the context of history, which can give us good priors. For example, there is a long history of intelligence agencies intercepting letters and post. Based on this, we might think it likely that they would seek to build similar capabilities with more modern forms of messaging.
In a similar vein, it seems that if one country is interfering in elections, engaging in industrial espionage, or spreading misinformation, then many countries are probably doing it.
These leaked documents are only a sample of hidden behavior. For example, if the DHS has a revolving door with Twitter, and other social media companies have law enforcement portals beyond their legal requirements, then it's safe to guess that most social media companies have a close relationship with their countries' intelligence agencies. It's just that they haven't all suffered leaks.
For example, if the DHS has a revolving door with Twitter, and other social media companies have law enforcement portals beyond their legal requirements, then it's safe to guess that most social media companies have a close relationship with their countries' intelligence agencies.
The DHS is not an intelligence agency. The fact that there's a lot of DHS-lead censorship in the Twitter files but not a lot of CIA-lead censorship could be an update against the CIA doing much of that.
One of the interesting aspects of that leak is that everything is so incredibly complex of who did what. There was a great talk about the Chaos Computer Congress called "Die Wahrheit und was wirklich passierte" (in English the truth and what really happened) and one of the points it makes is that one way to prevent things from being known to the public is simply to make them so complex that nobody will understand them. Having hundreds of institutions involved in the censorship industrial complex is one such thing.
It's easy to just think "well it's the intelligence agencies doing bad things" but the reality is about the complex interplay from a lot of institutions with funding from different sources. Funding comes from governments, companies, and billionaires.
There was a great talk about the Chaos Computer Congress called "Die Wahrheit und was wirklich passierte" (in English the truth and what really happened) and one of the points it makes is that one way to prevent things from being known to the public is simply to make them so complex that nobody will understand them. Having hundreds of institutions involved in the censorship industrial complex is one such thing.
This is basically the plot of Syriana.
I watched the film I think the real world is much more complicated. I remember Matt Taibbi saying that he counted 300 organizations in the Censorship Industrial Complex. Syriana has fewer agents than that.
You can't make a movie telling a good story with 300 organizations and it's also hard to write newspaper/substack articles about it.
Of course, but the primary theme of the movie is that no one has the full picture of what's going on.
They are almost the opposite to conspiracy theories
I'd like to add a warning that even if something is "almost the opposite" to conspiracy theories, many people's reaction will be very similar. Disagreeing with the mainstream is used as a heuristic for detecting conspiracy theorists; it doesn't matter what made you disagree -- whether you believe some bullshit, or you researched legitimate leaked documents and updated accordingly. For most people, both seem the same.
So, ironically, becoming more rational about politics can make people around you start seeing you as a conspiracy theorist.
As rationalists we seek to understand the world, but it's made harder by political bias and different agendas.
Leaked documents, represent a kind of ground truth, showing how the world really works. Telling us what's for sale, what the real agendas are, how powerful spies are, and how coordinated governments are. They are almost the opposite to conspiracy theories, as they present observations that can prune conspiracy theories.
But there are too many documents to read, so let's compare notes. What surprised you and caused you to update your view of the world?
Update: related conversation on TheMotte.org