I don't have much to add that's original, but as the site's official short person, I thought I should make my presence felt.
Excessive height always attracts attention. The only example I can think of is one I'm sure most people won't get, but, for example, look at Peter Crouch on the football pitch. He just sort of... towers. It draws the eye. Tall characters are there to stick out from the mundane.
In addition, height is desirable. The typical attractive man is
tall, dark and handsome (two out of three ain't bad, is it?
). I'm not sure how relevant it is, but I always feel that in emphasising height, Tolkien is saying "this person is attractive." Look at the list - Galadriel, Aragorn, who wed an elf, Thingol, who bagged a Maia. Tall equates to hunky in the men, noble in the women. Sauron also fits in with this; he appears as a tall man when he wants to seem fair.