[Thinlómien]

We have Faramir, who is said to be taller than his companions.

We have Éomer, who is the tallest of his éored.

We have Thingol, a mighty king and the husband of a maia, who is the tallest of the Children of Ilúvatar.

We have Maedhros the Tall who is the most powerful of the sons of Feanor and their leader.

We have Galadriel, the most powerful elf in Middle-Earth, who is very tall for a woman.

And there's surely a lot more examples...

Why? Why is Tolkien over-using this trick? Why are these persons tall? How does it affect them/the story?

And two bonus questions: is the fact that Aragorn is taller than Boromir important? Why? And consider Merry and Pippin. They became leaders after growing not only mentally, but also physically...

My only theory is that the height is there to emphasise the person's importance and high rank, and to sort him out of the rest.