I haven't done this, but think I'll start doing this in the coming season: logging injuries. This would include knowing who got what type of injury when, and how long did it last. Here's an example: I had several players get shin splints this past season - not just the-front-of-my-shin-hurts, but sitting the bench for a week. In getting ready for this season, I want to change the conditioning plan, but can't remember when those shin splints appeared and for how long. Knowing that would allow me to know when to back off for better recovery. Also, I've been thinking about hiring a physical therapist to assess player conditioning. Having a record of injury may help that discussion with the therapist and layout a case for the board.
Yup, going to be tracking that this fall!