To explain how an SLA helps i.e. empowers various stakeholders, let's assume some of them:
- Service Level Manager and operational team - SLA provides them with objectives which need to be achieved (e.g. resolution time for incidents of priority 2)
- Management of the organization/company - SLA is obligation to the customer and management want's to know whether company fulfills its requirement. Additionally, SLA is a tool to evaluate operational team (do they fulfill SLA requirements or not or whether we are much better then agreed in SLA so we can introduce new service level package)
- Customer - they know what to expect and they can control delivery of services they pay for (i.e. check whether they get what they paid for
- Suppliers - although not visible in SLA (or they don't know the content of SLA), but indirectly SLA defines their obligation, too.