It may not work like that. Some people don't want to work every week, some people have other jobs, may also be self employed and so on. As I have explained before, when I worked in the NHS, we used zero hour contracts to keep staff who didn't want to do regular hours on the books. One lady used to live with her husband in Hong Kong, another was self employed, another one owned and ran a hotel with her husband. If they wanted to work, they would contact us and say when they were free, if we wanted them to work, we would contact them and ask if they were available. keeping them on a zero hours contract meant that they didn't have to do the NHS induction package every time they came to work for us, and meant that their names stayed on the payroll so there was no delay in paying them.