Who marks their scores most: the most sophisticated musician, or the beginning chorister?
In my experience, the smarter the choir member, the more they use their pencil.
Young musicians need to be told what to mark. Mature musicians make marks as they read or rehearse, without being told. Professional musicians can mark scores intuitively, before they even sing the music.
We simply cannot remind our students enough: mark when decisions are made, mark any mistake you make more than once, mark anything personally difficult. Mark tricky pronunciations, mark breath points, mark reminders to look ahead.
Mark the score! Mark the score! Mark the score!
In the words of Dr. Jerry Blackstone, “Great choirs use their pencils; amateur choirs use their memories.”