[Boromir88]

I think Tolkien uses "tall" in several different ways through the stories. I agree with narfforc and Farael in that someone being tall is a sign of superiority. Not in the bad sense, but in a way that a natural born leader is someone tall and commanding. They are above the "normal."

I'll take Napolean for example. A brilliant leader, but Napolean's struggles were partially caused by his height. Because someone that is leading and commanding it's unusual to see someone 5'4''. The typical idea of Kings is someone that is tall because it appears more "kingly" a sort of benelovence.

But also Tolkien uses height to install fear and intimidate:

He laid his hand on the hobbit's shoulder in friendly fashion; but Frodo felt the hand trembling with suppressed excitement. He stepped quickly away, and eyed with alarm the tall Man, nearly twice his height and many times his match in strength.~The Breaking of the Fellowship

"You can say that I was too strong and took it by force. For I am too strong for you, halfling,"~ibid

Tolkien uses height here to install fear and intimidation, both with the reader and certainly with Frodo. Here is a guy that's twice my size and much stronger, what the heck am I going to do?

And he also does the same with Sauron:

Sauron should be thought of as very terrible. The form that he took was that of a man of more than human stature, but not gigantic. In his earlier incarnation he was able to veil his power (as Gandalf did) and could appear as a commanding figure of great strength of body and supremely royal demeanor and countenance.~Letter 246

So Sauron was in no means a giant, but he was taller and bigger than "human."

That is a great point with Merry and Pippin. They became tall for Hobbits, not only growing physically and that emphasizes the growth they made mentally...becoming more mature.

So, I think there are several uses for "tall" that Tolkien uses. The typical, Kings, leaders, warriors, are people who are tall and strong and kingly. Also, to emphasize a mature growth with Merry and Pippin. And then the "bad" use of tall, which causes fear and intimidation in those against you.

Edit: I must have cross-posted with Holby, but one thing she says caught my attention.

Another misconception is that the bigger the body, the bigger the brain therefore they are smarter.

What's interesting is that if someone is taller and stronger than you, you are at a disadvantage and have to find something to counteract it. Like I used with Boromir and Frodo, Boromir using his height to intimidate Frodo, so what does Frodo have to do? Frodo out wits Boromir and makes sure that he's always out of Boromir's reach so Boromir can't use that advantage:

Frodo did not answer, but moved, away till the great flat stone stood between them.

Frodo dodges aside and again put the stone between them.

Frodo plays it smart and makes sure that Boromir's advantage of height and strength doesn't come into play. He makes sure that there's an object between them and that he's out of reach.