When your CPU is working under high load it will generate heat approaching it TDP. If the heatsink of the cooler is clog with dust and debis or the fan is not working well the CPU will over heat. You do not want this to happen!

Spin the fan with your finger it should spin freely and without noise, resistance.

As you can see a lot of dust had built up under the heatsink, even though the top had recently been cleaned!

How far you go in cleaning the heatsink is your decision. I removed the Fan assembly to clean it thoroughly.

The Fan assembly was held on with four plastic clips. very carefully use a flat blade screwdriver to pry the clip up a little and push the assembly up, repeat until the fan assembly comes off.

Remove the metal plate in the center of the heatsink. Clean it and put it somewhere safe. You do not want to loose this inside a vacuum cleaner!