I haven't had the time to read anything other than second-hand commentary on the WikiLeaks document dump, but as "revelations" go, this one seems to be weak tea. The direct effect on the Afghanistan War will most likely be felt in some of the relationships the U.S. must manage (Pakistan and India, for instance). There's also the risk that some of the granular information they contain, which extend to some NATO coalition partners, could accelerate the crumbling of support in Europe.
Beyond that, as Joshua Foust noted, there is the human cost faced by Afghan informants and other strategic assets whose identities have been compromised, and the systemic risk of the intelligence community viewing information-sharing with an even warier eye.
More than anything, though, the documents serve as yet another reminder that war requires secrecy, which by definition means hiding the truth. Sometimes that truth is hidden by government classification, while at others it is simply obscured by an overwhelming mass of data points and information overload.