This document should be used in situations where the nature of your business means that you are unable to predict exactly how many staff you need to work at any one time. This agreement is similar to a normal contract of employment in that it sets out rights and levels of wages etc, but it makes clear that you cannot guarantee any set hours that the worker will be required to work.
These sort of contracts are often used in seasonal or retail working environments where business can reduce at certain periods. Although some controversy has been associated with the use of zero hours contracts, they are an effective way for small business that rely on seasonal business to manage their staffing levels whilst ensuring that they remain profitable.