Job documentation is the record of what was asked for, what was found, what was done, and what state the site was left in.
The four points worth recording
At booking — what the customer reported, in their words, and enough detail to send the right person with the right parts.
At assessment — what was actually found, which is frequently not what was reported. A site survey on larger work is this step formalised, and it is what an accurate estimate rests on.
During — anything discovered that changes the scope, recorded before the extra work is done rather than after — see change orders.
At completion — what was done, what was left, and photographs.
Why photographs matter more than anything else here
They settle disputes about the condition work was left in, they defeat most chargebacks, and they are evidence that reasonable care was taken — see liability and negligence.
Before and after, dated, taken as routine rather than when somebody expects trouble. Taken only on difficult jobs, their absence on an ordinary one becomes the point of argument.
What it does for the numbers
Job costing is only as good as what was recorded against the job. Labour hours and materials captured at the time produce a real margin; reconstructed later they produce an estimate.
That is what makes job margin variance worth reading.
Keeping it proportionate
A short structured record on every job beats a thorough one on some. The test is whether somebody who was not there could tell what happened.
Retention
Job records support warranty and defect claims for years after the work — see record retention.