The fixed round has a flaw at the root: it treats everything as if it were the same. The toilet with two hundred entries and the one nobody used get exactly the same pass, at the same time. The result: waste on one side and a service failure on the other — at the same time.
The maths of the alternative is simple to grasp. If you know the occupancy and real use of each zone, you can move hours from where they weren't needed to where they're missing. You don't take away quality; you take away dead time. The same coverage, fewer hours — and since labour is the biggest cost of any services company, fewer hours is straight margin.
In practice: you clean what was used, at the frequency the use justifies; you reinforce the team where there was a peak; you leave the room nobody opened alone. The round stops being a blind route and becomes a list prioritised by what actually happened in the space.
The honest caveat: "by need" isn't "clean the minimum". There are deep cleans that are by calendar and full stop — hygiene, safety, contract. Service-by-need applies to the layer on top of that base: where to reinforce, when, with what priority. Anyone selling it as "cut cleanings" is selling it badly and wrecking the service.
The fixed round charged for presence. Service-by-need charges for outcome — and proves it. It's a change of model, not an efficiency trick. And the provider's side wins twice: it spends fewer hours and has an argument the price-per-hour competition doesn't.