This may seem an obvious question, in which case I await to be pointed in the correct direction. However I've been considering this ever since I booked a fully-flexible ticket earlier this year.

In short: I'm struggling to see where fully-flexible is actually worthwhile. When I booked my FF ticket it was in the belief that travel was less than 50% likely. Indeed it was cancelled, so I got a full refund.

However, it then occurred to me that:

• Fully-flexible tickets are designed to give <duh!> flexibility when travel plans are not fixed. Therefore, they allow the holder to change plans at a moment's notice.
• Had I instead turned up to the airport a few hours before travel and bought the cheapest available Y ticket (though, in practice, this may equally have been B or H; semi-flexible) a few hours before boarding, the ticket would probably [true?] have been cheaper than the equivalent FF ticket booked months before.
• Of course, had I then had to cancel my plans, the ticket would have been wasted. However, if it was simply a change of date then B or H-class tickets would have been fine.
• Therefore, FF tickets are only worthwhile when you aren't sure until you are at the gate whether travel is going to happen or not?!? If you know any longer than 2 hours before departure, or if the date is flexible but the destination is not, FF is a waste of money.

What am I missing? Please discuss...

Edit: I've just thought of one perceived reason; that it gives a sense of being able to get a seat on a busy flight. But my understanding is that, if the flight is full, you won't be able to move to that aircraft anyway.