It matters because it is increasingly the thing an enterprise buyer asks for instead of a questionnaire. Having one shortens procurement and, more usefully, means somebody outside your business has looked at how you actually operate.
There are two kinds and only one of them is worth much. The first assesses your controls on a single day; the second assesses whether they operated over a period of months. Buyers who know the difference are asking for the second, and a report that does not say which one it is usually means the first.
The common mistake is treating it as an audit to pass rather than a year to run. The report describes a period, so the evidence has to exist across that period — the access reviews that were actually done, the tickets that show the process being followed. Preparing in the last month produces a finding, not a report.