Many times I have lit a show and have been so exhausted after the job that I just tore down the lights and headed home. It's only months later that I come upon a similar job and wish that I had made some notes on my last ideas. This is not to say that you should always duplicate the lighting setups that have worked well for you in the past. I intentionally change aspects of even the simplist of setups to experiment and discover new lighting ideas. But it is the more complex studio and location setups that justify you taking some notes.
Most business people keep a file folder on large, complex jobs that they are involved with.
Many setups contain special rigs or placements that create an especially nice lighting effect. For this reason, I often take still photographs for further documentation. Using the overhead diagram approach, as I often do in this column, helps you to realize and clarify what it is exactly that you do with your lighting. When working out an approach prior to the shoot, this type of diagram helps you to make a list of exactly what type and how many instruments you need for the job. It's sort of like a visual chck list for your shoot.