When you want to govern a service, or a group of services, through the life cycle, but you don't want to be overburdened by bureaucracy.
Put together a central cross functional service management team. This team should be broad enough to have all relevant competences and perspectives to answer all questions about what is the most meaningful to happen with the service.
The service management team doesn't need to have the competence to actually realize it. For that you put together service maintenance teams (for instance service desks, service development teams or service operation teams, or combinations thereof). The maintenance teams should have all needed competences to realize what the management team prioritize. In order to avoid handovers, and to keep a broad and deep knowledge level in the management team, representatives from the maintenance teams must be parts of the service management team.
While the identification of several roles and different groups in life cycle management frameworks such as ITIL or PM3 is important, it is also observed that this can lead to unnecessary organizational complexity.
There are basically four responsibilities when taking care of a service: managing capacity/capabilities and changes thereof, and when things go wrong: managing the incidents and solving the underlying problems. Instead of appointing different managers for these processes you can put together a single management team (of maximum 9-10 persons ideally) that is capable of making all decisions regarding resource allocation, policies, and prioritization. Then let the team sort out how they distribute responsibility among themselves, or if they should delegate some of it to others.
The management team should work closely with the maintenance teams, having representatives present when the maintenance team plans and follow up on their own activity, and having representatives from the maintenance teams in the management team. In order to keep it agile we must minimize handovers, align the mandates with the abilities, and always make our decisions based on empirical evidence and deep understanding of what is happening on the floor, close to the customer. Both the management team and the maintenance teams are regarded as governance teams that collaborate in governing the services.
All common agile principles about transparency and self-organization apply here.
The management team should maintain the vision and the plan. The plan should be continuously updated with correct data about velocities so that forecasts, if you need them, are kept accurate. Experience has shown that this can be accomplished if the management team meets regularily 1-4 times a month.
Groups like the management group are prescribed in a lot of frameworks. What we've done in order to keep it agile is basically to merge all these groups into one. The idea of assigning responsibilities and accountability to a group, and then let the group sort out how they distribute the responsibility, is a common organizational pattern in team focused lean and agile. Having mutual representation between two groups is used in sociocracy, a governance system based on self organization. Emphasis on cross-functionality of the teams in order to reduce handovers and improve lead time is a common Scrum construct.