Many tea shops print an elevation next to their teas, and it is fair to ask whether that is information or decoration. It is information — but not for the reason most shops imply.
Slower is the whole point
Higher gardens are colder. Colder bushes grow more slowly. A leaf that takes five weeks to reach picking size instead of three has more time to build up the sweetness and aroma that survive processing. That is the entire mechanism: elevation is really a stand-in for time.
You can taste the difference side by side without any training. Brew a high-grown oolong against a low-grown one made from the same plant and the high-grown cup will be sweeter, thicker in the mouth, and noticeably less astringent. It will also last two or three infusions longer before it gives up.
Where the number stops mattering
Past a certain height the returns flatten and the risks rise. Frost damage, transport difficulty and short picking windows start to cost more than the extra slowness buys. Some of the best teas in the world come from gardens at quite modest elevations, and they are worth it because of the plant and the hands that finished them, not the altitude.
Mist matters at least as much. A garden that sits under cloud until midday behaves like a garden much higher up, because what the leaf actually experiences is diffuse light and cool air.
So why mention it at all
Because it is something a curious drinker can look into, while most of the vocabulary the tea trade uses cannot be checked at all. Anybody can write “premium” on a pouch. Saying plainly where and when a tea was made is a claim that has to survive scrutiny.