I’m not super-well read on the federal FOIA, but am responsible for public information requests at my city, which follow state regs.
At least at my level, the big one is that the government does not have to create documents to satisfy a request. If the data is not in a readable format, we essentially don’t have responsive data and are not required to go through the conversion process because that would be creating data.
We also have a rule regarding conversion of electronic data from internal proprietary format to something the requestor can read that allows us to refuse if responding to the request would cause an undue disruption to city services.
My example of when we used it was a request for every copy of a specific formthat had been rejected in building applications. It would have required manually scrubbing tens of thousands of building permits to look for specific forms that were not always turned in using the same name and looking for versions that were rejected (which may have been part of accepted applications if the applicant corrected the form later).
It would have taken about 6 months for a full-time employee, and our city only has 11 staffers, so we were able to tell them “no.”