It's to avoid corruption.

I worked for the equivalent of the IRS for two month in my country (student job basically). When people asked for a deferred payment, i could accept it if it was the first time, but when they asked for a deffered payment the second time, or for reduced taxes (recent job loss, loss of a house or big events like this), i had the mean to verify who the person asking for this was, but not the mean to approve it.

I verified the information and filled a form, then asked for approval. The person approving had no idea who the person asking was (he had no access to the tool i used to match the internal ID to an actual person), but had the form i filled, and approved of the deferred payment/reduced taxes without any knowledge of who asked. Also i did not know who that person was, and he did not know who i was.

All of that is not very effective, but it reduces the risk of corruption from civil servants: you either have limited information, or limited power (this isn't the case with mayor or other elected officials though).