Pros: You can daydream about using your miles.
Cons: Only a few seats per plane and you can never reserve one.
I've been in AA freq Flier program for years.
Every time I want to fly somewhere, there are no seats open for Aadvantage customers.
They probably have like 2 seats per plane and once those fill up, it won't matter if the rest of the plane is empty, you can't use your frequent flier miles.
Forget about hawaii. You'd have to call up the same day tickets for a flight become reservable (about a year in advance).
I don't plan my vacations that far ahead. If your life is that pre-programed, you may be able to use your miles. I have wound up giving them away to retired relatives who can plan 4-12 months ahead.
Just one more reason to hate the experience of flying.