It's known to be a stat that tries to do too much, but there are very useful things you can do with it.

Unless you're playing against hudbots (rare at micros, if that's where you play) you can get away with cbetting like a monkey and run a 6+ AF without worrying about exploitation.

If you find an opponent with >6 AF tho, you can assume they've got a much weaker range when betting post flop.

If you find someone with <1 AF, they're probably a calling station.