A Service Level Agreement (SLA) is essential in cloud services as it defines the expected level of service between the provider and the client. It outlines key metrics like uptime, response time, and support availability. SLAs provide clients assurance of the services promised and serve as a basis for accountability, enabling them to understand their rights and responsibilities. They also play a critical role in resolving disputes by clarifying expectations, which fosters a beneficial relationship between the provider and client. Ultimately, SLAs help ensure service quality and user satisfaction.