A wet lawn will clog the mower and slow down growth of the lawn.
Wet soil is soft and easily compacted by the weight of the lawn mower.
The root system is deprived of air in compacted soil, leading to a thin, weakened lawn. Mow when its cool. Mowing during the cooler part of the day helps grass grow better. Root development is best when the soil is cooler. Mowing during the hotter part of the day exposes the soil to the sun, slowing root growth.