The Freedom of Information Act has been an important journalistic tool since its enactment, but sometimes a request for government records can involve information of a highly sensitive nature. National security is a high priority within the United States government and a FOIA request can include protected information that may jeopardize national security interests or put American citizens in harms way.
Judges tend to side with the petitioning journalist in cases of a FOIA request, so it is important for the respondent government agency to present a compelling case for denial if that is what they seek. A Freedom of Information Act request is not always automatic on local levels either, as some of the agency deliberations done informally may also be considered protected information by the court.
Records that are held by local and state agencies are also often not subject to FOIA filings when they are part of an ongoing case and could hamper government interests in filing a criminal charge against a suspect. These are not always as obvious as the potential for national security that the federal government generally claims, but can be detrimental to anyone who has filed a criminal complaint that may be accessed by the potential defendant.