Two parties working in sequence, neither watching the other
Venue staff close down, complete their tasks and leave. The contractor arrives afterwards and works on a space it did not see before the close-down. If something was not done, the contractor either absorbs it, skips it or reports it, and in the absence of an agreed process the first of those is the most common outcome. That absorption is invisible, unpriced and it steadily changes what the contract actually covers.
The reverse happens too. A venue arriving in the morning to something unsatisfactory has no way to tell whether the contractor missed it or whether it was left in a state the contractor was never contracted to address. Both parties end up arguing from impression, and the argument recurs because nothing about the underlying process has changed. A short record at the handover point resolves both directions at once.
