A managed service means paying a provider to run the network rather than staffing it yourself: monitoring, updates, scheduling, and getting a technician to a broken screen. It converts an operational headcount problem into a contract.
It usually makes sense in two situations: a network too geographically spread for an internal team to reach, and an organisation where nobody actually owns the screens, which is how networks quietly die. A contract with a response time is a stronger guarantee than an internal intention.
The caveat is that the interesting clauses are about the things people forget to ask. Response time to a dark screen is the obvious one; the ones that matter later are who owns the content, whether you can export your own asset library, what happens to your player configuration if you leave, and whether "monitoring" includes anyone acting on an alert or merely recording it.
Beware of a managed contract used to avoid the content question. Nobody outside the business knows what this month's promotion should be, and the most common failure is a perfectly maintained network showing content nobody has refreshed since launch.