the main question SLOs trying to answer is if reliability is a feature how do you prioritise it versus other features? setting a target for system reliability and communicating that target widely allows all parts of your organization to determine independently whether or not the service is reliable enough. Acknowledging that a specific quantity of unreliability is acceptable provides a budget for failure that can be spent on developing and launching new features and the remaining budget provides a signal defeat into your planning cycles to ensure work to improve reliability is prioritized.
SLOs provide a common language and shared understanding between different parts of your organization anchoring the reliability conversation on concrete data.
SLOs are not only an operational concern but for them to function correctly as a prioritization signal the target must be set in conjunction with engineering and product teams. everyone must agree on the desired experience of your users.