SLA and stakeholders

Answer:
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.

Read the articles
"SLAs, OLAs and UCs in ITIL and ISO 20000" https://advisera.com/20000academy/knowledgebase/slas-olas-ucs-itil-iso-20000/
"ITIL – Service Level Agreements: Designing frameworks" https://advisera.com/20000academy/blog/2015/01/27/itil-service-level-agreements-designing-frameworks/
"ITIL Supplier Management and Service Level Management – How to put the two in balance" https://advisera.com/20000academy/blog/2015/11/10/itil-supplier-management-and-service-level-management-how-to-put-the-two-in-balance/
to learn more about SLA and other contracts.