In general, gap pads on critical components may be sufficient cooling for embedded systems in the low power segment, around 5W, even though the enclosure is closed.
- If there's some kind of air flow inside the box it may be good enough to take the heat away.
If not, as in this case, there are a handful of additional heat dissipation methods: Heat dissipation through a metallic enclosure, heat sinks on components or on the exterior of the box, heat pipes for heat distribution, inlets and outlets in the enclosure to increase the air flow or a fan.
Cooling with a fan is sometimes necessary, for example to design a powerful and yet compact system, but there are drawbacks.
- It makes noise. It can break down. Airflow comes out and dirty air is forced into the enclosure.
The suggested alteration in the example was to introduce holes in the cover. That would enable air to flow in through the bottom of the enclosure, through the interior and electronics and out on the upper side distributing heat for increased cooling.