Keeping notes on a player can be very valuable.
Especially if you are always playing the same games day after day.
If you get beat in a hand by someone just luck-boxing on you, make a note.
If you see a player consistently making the same move time and time again,
always defending their SB, making the standard raise every time they are on the button,
make a note
If you have a HUD going you can decide after a session to go back and look
at various players actions. You just might pick up some tells
If you have one player who you just CAN'T beat, go over the hands played against them.
Did you play too aggressive and not see them showing strength?
Did you allow them to get to a winning hand on the river by trying to trap?
Then the next time you see them you will at least have some idea of their style.
Use the color coding on PS or FTP to identify the fishes, the sharks,
the loose and the passive player.
Pick one color to represent friends and one to mark the villains
but don't allow these notes to become a 'Bible' on how to play.