It makes two quotes comparable
Ask three local providers to quote a small premises without a document and you will receive three different jobs at three different prices, with no way to tell which is which. One assumes the kitchen is included, another assumes fortnightly glass, a third excludes the store entirely. The prices then differ for reasons nobody can identify, and the cheapest wins by default. You are then choosing between three interpretations of your premises rather than three prices for the same job.
One page with the rooms listed, the tasks under each and a frequency against them converts that into a genuine comparison. It takes half an hour to write and it is the only thing that makes the exercise meaningful. For a small business buying cleaning perhaps twice a decade, that half hour is the highest-value time in the whole process. It also gives you something to hand the next provider without repeating the whole conversation from the beginning.
