If you look at FOIA litigation in only the context of who ultimately wins a case, you would come to the conclusion that the government routinely is the complete victor. That conclusion, however, would be wrong.
The results of FOIA litigation are much more than just a judge's opinion for one of the two sides in the case. Bringing a FOIA case often results in a more timely release of information, more information being released then the agency would have released if it wasn't in litigation and more information going to the requester about agency decisions and withheld documents.
Many agencies have backlogs of FOIA requests. Under current law, to justify not processing a request pursuant to the statutory time periods, an agency basically has to show that its backlog was unexpected and that it is working to reduce the backlog. When I was with the FBI, we called it a "due diligence" declaration. Agencies are not required to tell requesters who are not in litigation when their requests will actually be processed. However, when seeking a stay from the statutory time period, the agency must ask a court for a stay until date certain. Thus, the requester will win by just having some certainty as to when his or her request will be processed.
Agencies won't admit it, but times for processing cases in litigation are bumped up. This is because agencies don't want to ask for so much time that the court will deny their requests as ridiculous. Additionally, some judges will cut the time agencies seek in many cases, pushing the requests ahead, even if the agency can show it meets the standards required for a stay of processing.
Often, where there is no litigation, an agency will deny, deny, and then deny some more. However, when a judge and a U.S. Attorney are looking over their shoulder, agencies tend to release information where the withholding was iffy rather than force a court to order its release. In some cases, agencies will drag out these releases on an issue by issue basis, resulting in releases of thousands of pages that the agency did not intend to actually release but was forced to because of the litigation aspect of the request.
Finally, even where no actual documents are released, requesters learn a great deal through the litigation process. Agencies are required to produce Vaughn indices justifying their withholding decisions. They are not required to do this during the administrative stages of the request. These indices describe the documents in detail, often answering questions requesters may have about an agency process even without the release of the document. Thus, even in these cases the requester can get a victory by the information learned from the agencies justifications of its past actions.
So losing a FOIA case isn't usually a complete loss for the requester. In fact, most of the time, the requester has much more information because he or she chose to file suit than if the party had not.