It's a measurement. In a vacuum, it is fairly useless. Just because someone is tall, it doesn't mean he can read defenses, make decisions, throw, or run. GAIII and his brother are very fast; as of now, they are not very good football players.
If you evalute two players and find they are pretty even, then maybe the fact that one is four inches taller than the other may become an important factor. My sense is that is the exception rather than rule.