Transpiration is supposed to help the plant in the following ways.
1. Excess water getting into the plant might decay the cells. Transpiration prevents it by removing the extra water.
2. Extra quantity of water, if retained would disturb the osmotic relationship between cells. This is prevented by transpiration.
3. Transpiration stream helps in the distribution of nutrients to all the parts of the plant body.
4- Fresh and cool water reaches all the parts of the plant body and this reduces the metabolic heat acting as a coolant.
5- Transpiration indirectly helps in the uptake of salts as the latter get into the plant together with water.
6. Upward movement of water (Ascent of sap) is due to the suction force created by transpiration.