Everyone has a drawer of appliance manuals. Nobody has ever opened it. Meanwhile the two facts that are genuinely irreplaceable — what exactly this machine is, and when it was bought — are on a sticker behind the unit and on a receipt that faded three years ago.
What is actually worth keeping
The model and serial number, because that is what a warranty claim, a spare part, and a recall check all key off. The purchase date and price, because that decides whether a repair is worth it. The installer or retailer, because that is who you call. Nothing else.
Photograph the plate, not the paperwork
The serial plate is a photograph and thirty seconds. It is worth doing on the day something is installed, while the machine is pulled out and the sticker is visible, rather than in five years with a flashlight and a bad back — which is, reliably, the moment you will need it.