Service Level Management is a formal way for setting customer expectations BEFORE the customer has the need to request service. It is a methodology for introducing and implementing reasonable expectations between you and the customers you support. These are most often contained in a document called a Service Level Agreement (SLA). The SLA establishes a two-way accountability for service, which is negotiated and mutually agreed upon. It is really a contract that documents operational and interpersonal relationships, establishes mutual expectations, and provides a standard to measure performance.
Without SLAs in place, you are effectively telling your customers that you will provide support to them, at any time, under any conditions, without any limitations to the systems and services they have. However, this is not the worst part. The worst part is that you cannot possibly ever meet your customers’ service expectations because every customer will have a different expectation and that expectation will change every time they call.
Here is a great White Paper on Implementing Service Level Agreements. See https://www.givainc.com/wp/it-help-desk-software-cloud-whitepapers.cfm