One blatant example: how do you think it'd benefit intelligence agencies to see who begins encrypting their comms after the news breaks?
If it's a topic of talking head discussion on the news, and nobody picks up arms, that's implied consent. "Well, that's just normal operations, we've been doing that since 20xx!"
Open secrets are ones you don't have to worry about leaking in ways you don't want. Being able to coordinate media reaction, social media reaction, and Gov officials' responses, is key, if this was indeed a limited hangout.
Another advantage I omitted (for fear HN would not comprehend it) was simply the bragging rights: look at this awesome spy tech we have, wouldn't it be a shame if someone - used it to advance their national interests. And while you're all gawking at it, don't none of y'all get to thinking that Murica got weak. We're talking to you, "allies."
It's funny to think that the spies who know the biggest truths are also the ones who need to be the most emphatic in their denials of them. Must be such a weird life. To have a reputation as being unreliable in everything except lying. Crazy.
Thankfully regular people don't know their own beliefs are untrue. The counter-narratives are designed so well that regular people readily accept them, and vigorously self-censor dissenting ideas. The system works! :P