The purpose of this is to get paperwork and other evidence from the landlord to help prove your case. Basic things like any papers concerning the terms of the rental agreement, the ledger of payments and charges, communications between you, and the evidence they have to support their notice, are naturals for this. It can also be used to get information like the deed to the property, the management agreement, communications between the owner and management, receipts for repairs, mold reports, bank statements, building permits, pictures, security footage, and other paperwork that the landlord doesn't want to disclose. This is the way to force the landlord to give you this, even by court order if necessary.

When used together with requests for admission or interrogatories, it can require them to give you the paperwork that they identify as proof in those other. With these responses, you may find the proof you need to win that case, but at least know what they are going to claim at trial, to you can bring your counter-proof.