How does transpiration help in sucking water up?
The benefit is not in taking up more water but in transporting the things that water contains.
Plants rely on bulk transport in water flowing though specialized tissue (xylem), somewhat analogous to blood flow in an animal. Water flows through the xylem using capillary action; when water is lost at the top, capillary action pulls water into the vacated space and the flow continues down the entire height of the plant. Water removed for other uses like photosynthesis also contributes, but transpiration is important for many plants to increase the flow rate.