Reliability-Centered Maintenance (RCM) is a framework used to analyze a system's failure modes and define how to prevent or find those failures early. RCM can be used to create a cost-effective maintenance strategy to address dominant causes of equipment failure.
Proactive maintenance tasks consume time and resources, so they are not something you want to be doing unnecessarily. The Reliability-Centered Maintenance framework helps ensure that the cost of proactive maintenance does not exceed the cost of the consequences of failure. This article by Brendan Casey of HydraulicSupermarket.com describes an example where preventative measures paid off in the long run.
This article from IDCON, INC. warns that Reliability-Centered Maintenance can be overkill for some pieces of machinery. The author believes it is most useful when designing, selecting, and installing new systems in a plant, and when setting up preventive maintenance for complex equipment.
Reliabilityweb.com offers this detailed article with specific steps for both preventive maintenance and corrective maintenance on a hydraulic system. They also provide several tutorials geared to the subject of Reliability-Centered Maintenance.