[sirana]

I think the point is: If he had an 5.0 aggression, you would know that he is aggressive postflop not because of the statistics, but because his constant betting and raising. It says much more about a player if you know e.g. that he has raised a gutshot on the flop or checked TPNK, than if you say he has aggression factor this or that.

The aggression factors are good to supplement actual reads, but to base a play on a stat (especially a windy stat like AF) makes you likely to play suboptimal poker.