Ventilation Plugs are used for equalizing the pressure inside and outside the enclosure. The same is achieved with the help of a membrane inside the ventilation plug, which allows for gases (air) to pass through it while blocking liquids and particulate solids (dust).
Applications / Benefits:
These prevent components inside the enclosure from being exposed to pressurized gases when the enclosure heats up. (By virtue of pressure equalization)
These also prevent generation of vacuum inside the enclosure when a heated enclosure cools off. (E.g. In luminaires)
These help maintain IP 68 rating of the enclosure while allowing for the above benefits.