Question

why is transpiration useful to plants?

Answer 1

for the loss of excess water

Answer 2

Heya,

Answer to your question is:-

-» Transpiration is the process through which excess water from plant body is released through the stomata present on surface of leaf.

-» It helps in maintaining cohesion-adhesion tension, so that water can move through xylem up to leaves.

-» It also helps in cooling process of the tree.
In a way transpiration helps in cloud formation. Water vapour released will help in cloud formation also. 

HOPE THIS HELPS YOU:-))
@Ashu