It could lead to discriminisation of people (or topics). They should not keep the information about who requested what any longer than needed to fulfill the request.
I wouldn't be surprised if they were required to keep the info for auditing purposes to report on how many FOIA requests they get, if they responded in a timely manner, etc. If they dumped that info, I can see another group of people all pissed off that the government is hiding the stats about the whole FOIA request/response procedure. It really doesn't matter what the government does... there is always going to be some group of people that will complain about it.
