A site that can focus on preventive maintenance (PM) will be in control over the reliability and integrity of their assets and as such be able to plan the required budget and staff for keeping the plant running. The above figure indicates that for certain equipment that does not have significant failure consequences a managed run-to-failure policy is also part of a planned maintenance strategy. As such, it is important that the function and operating context of the equipment is well known and considered in the development of a PM plan . The objective is to arrive at planned maintenance tasks that are optimal in terms of budget, staff and exposure risks, as indicated in the figure below.

Maintenance effort vs. costs.
The following list indicates some examples of sub-optimal maintenance performance:
- Unasserted and non-context-based tasks;
- Plan based solely on vendor recommendations, similar equipment or individual experience without any consideration to environment or current condition;
- Plan based on equipment requirements, rather than functional requirements;
- Impact of failure to the plant not considered;
- Mostly time-based tasks;
- No common understanding amongst Operations, Inspection, Engineering and Maintenance about the approach; and
- No living program in place to update PM plans regularly.
Modern views about maintenance are characterized by:
- Failure mode analysis is key to determine the PM tasks that will be effective;
- No PM plan can raise the inherent reliability level of a design;
- It is not cost-effective to develop a PM plan for equipment without considering its actual operating context; and
- Maintenance is performed to maintain a certain function, to prevent premature failures or to mitigate the consequences of failure. It is not intended to prevent the failure itself.