If per-session notes work for you, go for it.
WK is mostly about pure memorization, though, there isn’t any real reasoning involved. I’m unsure of what I’d write other than “today felt particularly hard/easy”.
The system already tracks progress and accuracy each session and there are plenty of user scripts to aid with tracking.
There is a LOT of disambiguation required, though. I make heavy use of the meaning/reading notes on individual items.
Often I want to distinguish from one or more similar looking characters, so I might write all of them down in the notes for each character, copy and pasting my mnemonics to distinguish them. (The Niai user script is also a terrific help.)
Other times I just want to clarify which specific English meaning was intended or any other usage notes I might want to make.
You can’t see your item notes until you answer an item (correctly or incorrectly) but you’d only be cheating yourself if that weren’t the case.
In summary, I personally see little value in per-session notes, but per-item notes stored with the system have proven invaluable.