The above quote and others compare collecting miles to other kinds of collecting. There's one huge difference, however, that hasn't been elaborated on: Other collectibles can serve a purpose other than being sold/used. Miles do not.

For example, you don't need to sell a painting for it to be useful. You can hang it on a wall and admire it. It will serve some purpose even if you never sell it. This is true of other things such as coins or stamps.

But what about miles? Unless you get your kicks admiring FF statements or bragging to friends, miles have no use unless they're used.

It's certainly a good idea to save for that big free vacation, but I'd rather be lounging in Maui than admiring my banked miles on a computer.