Here's my $0.02 on the subject. Feel welcomed to chime in to share your wisdom...
ESMers (Enterprise Systems Management experts) are often charged with the responsibility of providing monitoring and availability information for services. But nowadays due to the influences of ITIL guidance and other best practices, it has become apparent to many, that it is probably insufficient to assume reporting the availability or status of a CI (Configuration Item) implies availability reporting on a service provided to a customer. In other words, when tasked with implementing a monitoring solution to provide availability and status information for a service, monitoring of ALL CIs critical to the usability of a service served to the end recipient MUST be considered.
An "IT service" can be defined as a specific output that provides customer value. It is a measurable product which is the basis for doing business with customer, and is deliverable through a series of interrelated processes, or activities, or both. It comprises of a group of related, CI delivered functionality required by a customer for business use. It is NOT available to a customer if the functions that customer requires at that particular location CANNOT be used. ESMers provide status and availability information to assist other IT personnel ensure the underpinning CIs for a given service are kept sufficient, reliable and properly maintained. They monitor a service, by monitoring in a correlated manner CIs that comprise an IT service. Internet, E-mail and Telephone are just a few examples of well known IT services that come to mind.
Since in general an IT service comprises only a limited number of CIs, monitoring and availability information should be focused on those CIs responsible for the service delivered to the customer, instead of everything in the environment has been traditionally.