Humidity monitoring is essential for flora and fauna to thrive As far as human beings are concerned, we transfer heat through our bodies using processes like perspiration and evaporation.
As airliners descend from colder altitudes into warmer air perhaps even flying through clouds a few thousand feet above the ground , the ambient relative humidity can increase dramatically.
Similarly, during summer in humid climates a great deal of liquid water condenses from air cooled in air conditioners.