USE CASE - TOO HIGH VPD (humidity too low)
Rate of evapotranspiration from the leaves can exceed the supply of water through the roots - the stomata will close and photosyntesis will slow down or stop. Leaves are at risk of high temperature injury, since evaporative cooling is reduced.
To avoid injury and death from wilting, many plant species will either curl their leaves or orient them downwards in attempt to expose less surface area to the sun. This can downgrade the quality of potted and foliage plants and can also reduce the growth rate and quality of vegetable crops.