How do you know what the temperature is where your router or switch is? This can tell you if the device is overheating due to fans being out or improver ventilation in the room where the Cisco device is. Additionally, you would want to know if the fans were running and what their speed is. Oh yeah, and what about the status of your power supplies?
You can find out all this and more using the Cisco IOS show environment command. You can also configure the switch or router to alert you when there is an environmental alarm.
To see how it is done, read my article Monitor Cisco routers and switches using the IOS environment command