Routes decide profitability. Eight properties in a day or five depends on the order they are visited in and on knowing how long each one really takes, and a round improvised each morning quietly loses a stop or two a week.
Readings have to survive an inspection. For a community pool, the chlorine and pH recorded on each visit is a legal record, and reconstructing a summer of readings afterwards is neither possible nor honest.
Each property is its own machine. Pump model, filter type, cover, salt system and the particular valve that sticks belong to a record for that pool, because the technician who knows it is not always the one who goes.
Chemicals are consumed unevenly. A shaded pool and one in full sun consume very differently, so tracking product per property is what reveals which contracts were priced too low.