A wax chart can give you a good start, but it does not know your skis, your technique or the tracks where you usually ski. Two pairs of skis with different camber can react completely differently to the same grip wax, and the same glide preparation can feel different in fresh snow and in a glazed recreational track.
A wax log keeps experience from disappearing between outings. The purpose is not to write a technical report after every session. Write enough that you can compare with the next similar conditions: what you saw, what you did, how the skis performed and what you would change.
Feel free to note the plan before the outing and fill in the result immediately afterward. Then you will also see when the forecast and reality differed. After five or ten sessions, patterns begin to appear. After a season, you will have built a wax chart that actually knows your skis.
Give each pair of skis a simple name or number and rate grip, glide, icing and durability from 1 to 5. Feel free to photograph the page with your phone. Then the note remains even if the book is left in the waxing room.