I have been making contact sheets for a very long time. First with 35mm then 6x6 and once again 35mm.
I fill out a developing sheet with each tank of film(s) going through. It only takes a few seconds to fill out and during this stage I carefully work out just what developing time(s) solution dilution, etc, etc,. At the end of the developing stage I write comments about the negatives. Later on when I do enlargements, I will sometimes make a notation or two, regarding any important points that may be due to the developing. These short notes are held in a large ring binder and currently go back 18 years. It is surprising how often I will look back to find the last time I developed a certain film after shooting under certain conditions, to look at just how the film came out. It really does help in deciding on what developing technique may be best
All films are contacted and the sheets then studied under a loupe. My wife often makes certain suggestions that I would have missed, as I'm looking to see if the shot I was after worked and miss the one that is good but I only glanced at.
Every contact sheet is numbered, dated and filed in an old 8x10" paper box, with the year number marked on the outside.
Having done a reasonable amount of professional work in which I sold enlargements of my films, every negative has it's frame number and if it's enlarged, that number goes on the back of the print and in any notes. I used to do this before I ever sold any work and even though I don't sell any work anymore, I just kept it up.
The best reason for doing a contact sheet without any manipulation, is that it is an invaluable aid to density when doing enlargements of a roll or rolls from the single session. One can instantly see if one negative is equal in density or perhaps an 1/8 or 1/4 of a stop different. For working prints it makes life really, really easy, especially if you have only an enlarger timer and your brains instead of analysers and probes.
Mick.