I kind of agree with Gonnif. I am personally maintaining a journal with the interesting info. I’d also advise not to procrastinate and complete your log the same evening or the day after any shadowing session you had (to make sure things are still fresh in your mind).
I see the log as a written memory and as gonnif said, it can be used in various circumstances. I don’t think there is any dos or donts but I just jot whatever I can. It will be useful at the time of writing the essays and even to refresh my memory in the fortunate event of an interview.