A post is a promise, and the rota is where it is kept
A static post on a client site is 168 hours a week of one officer, sometimes two. On twelve hour shifts that is four officers on four on, four off: two on days, two on nights, and the pattern walks through the calendar without ever landing on the same weekday twice. Add a second site, a mobile patrol, a control room and a relief officer who covers holidays and sickness, and the rota is a dozen people whose weeks never line up. A spreadsheet holds it until the first swap; then two people think they are on the same night and one post is empty.
The second thing is money. Nights are paid with a premium, bank holidays at a multiplier, and an officer who did five nights and a day at two different sites has a payslip that takes an hour to check by hand. The third is kit. Radios, keys, torches, body cams, the uniform: every one of them has been issued to someone, and when that someone leaves, the firm needs to know what is in their car.
Below is how a firm of twenty officers on three sites looks in InShift: every post on one screen, the four on, four off pattern as it really lands, the kit against each name, and an officer who sees only their own post and their own hours.