Notes are for ALL passengers, regardless of whether Skywards members and/or with or without status.
If a pax (no skywards / no status) is difficult or has a problem on a flight / has a birthday / loses something etc etc then notes can be added and attached to that passenger to forewarn others about behaviour and/or give chance for service recovery. Your behaviour will follow you.... and crew can determine when such notes expire.
EK is not alone in implementing this system.
The majority of passengers (and Skywards members) seldom have many notes unless they're complete .......s or unless they've suffered a service issue. Things like drink preference etc and aisle / window preference are all recorded in Skywards account page.