Even when the piece is memorized, more pencil in the score is a sign of a more polished performance.
I’m looking at a clarinet part covered in pencil markings – tempo, tuning, dynamics, circled spots, reminders to look ahead (drawn eyeglasses), emotional ideas. My guess is that only a small percentage of them were necessary in the performance, and my certainty is that the performance would have been less effective without them.
“I’ll remember” is confidence we don’t have time for. Especially if we want to tackle harder and more music, memory becomes increasingly fallible. Written notes save us and raise our performances.
Students: however much you’re writing in your scores, write more.