monitors and rules in operations managers

https://technet.microsoft.com/en-us/library/hh457603.aspx

Create a monitor if…

• You want to affect the health of an object. In addition to generating an alert, a monitor will affect the health state of its target object. This is displayed in state views and availability reports.
  
• You want to automatically resolve an alert when the error condition has been cleared. An alert from a rule cannot be automatically cleared since a rule has no way of detecting that the problem has been resolved. A monitor can detect that the problem has been resolved when the condition for its healthy state is met, and the alert can automatically be resolved.
  
• You are creating an alert based on a performance threshold. There are no rules available to generate an alert from a performance threshold. A monitor should be used for this scenario anyway since you can use the condition where the performance counter is under the defined threshold.
  
• You have a condition that requires more complex logic than is possible with rules. The Operations console provides a variety of options for setting the health state of a monitor but only simple detection for a rule. If you need more complex logic for a rule but don’t have a method to detect the monitor’s healthy state, then you can create a monitor using Manual or Timer reset. See Event Monitor Reset for more information.

Create a Rule if…

• You want to collect performance counters or events for analysis and reporting. Monitors only collect this information when it initiates a change in health state. If you want to collect the information you need to create a collection rule.
  
  If you want to both collect a performance counter and set a threshold for it to set a health state, then create both a rule and a monitor using the same performance counter.
  
• You want to generate an alert that is not related to health state of an object.