I do the same. If the conductor wants to deviate in an area (i.e. slow down more than expected, etc.) I will make notes. Any area that I tend to forget something I'll make note of that as well. The more experience you gain you know when you need (or should) notate helpful information. Always have a pencil or mechanical pencil with you. Very helpful. Never make notes in ink unless its your own property. Very irritating when someone makes notes in ink which is not courteous to others that may use the parts after you.
John 3:16
Conn Victor 5H Trombone
Yamaha 354 Trombone
Conn 15I Euphonium