Transpiration controls the rate of water absorption. It helps in the absorption of minerals andregulate the temperature. At the same time, it has disadvantages such as it leads water deficiency in plants and thus, impair the processes of photosynthesis and growth, etc. It is therefore said ‘transpiration is a necessary evil’.Transpiration is considered to be a necessary evil because it leads to loss of water from plants but provides the plant with several advantages as well.

Creates transpirational pull for transport

Supplies water for photosynthesis

Transports minerals from soil to all parts of a plant

Cools the surface of the leaves (due to the evaporation of water)

Keeps the cells turgid; hence, maintains their shapeTranspiration is necessary because it helps in transpiration pull that indeed helps in the transportation of water throughout the plant body. It is an evil because bulk of water is lost during this process.

Because it is an inevitable, but potentially harmful, consequence of the existence of wet cell surfaces form which evaporation occurs. ... Wet surface of leaf cells allow gaseous exchange.Transpiration affects indirectly the processes of respiration and photosynthesis.