"He did nothing wrong, therefore he has nothing to hide".
Are you really questioning the fact that this was made public while NSA, CIA and other agencies have been wiping their asses with the Fourth Amendment of the US Constitution and the Article 8 of the Universal Declaration of Human Rights?
Running with the Chelsea Manning leak helped start a conversation about the ethics of drone warfare and the culpability of the US military in the deaths of civilians.
What kind of a wider conversation does leaking John Brennan's SF-86 create? Maybe there's some ancillary discussion about those in the security community not using secure channels but it mostly just feels like a cheap shot.
Does it necessarily have to create a conversation?
It, at the very least, destroys yet another time the "nothing to hide" argument and underlines both the fact that nobody is safe unless active measures are taken and that all this spying business is tainted with serious amateurism.
And if this is worthless to you, see it as a backlash. Our personal informations are intercepted on a daily basis and played with in a way that we have no control over. The average Joe, alone, can't fight back, Wikileaks is the collective answer.
It is in-line with Trevor Paglen's work [1] on demystifying spying activities: they're no super heroes, they're bound to physical, practical and logistical limitations (like we all are), we can fight them.
[1] (video) "Seeing The Secret State: Six Landscapes" https://www.youtube.com/watch?v=mF4vQA7eWgE