Clojurians Log v2

Another point of confusion is that in all the examples I can find it seems the same keywords seem to be reused:

...
:model   [[:amount {:id :amount}]
          [:total {:id :total}]]
...

Presumably these keys (`:amount` and :total) aren't just repeated for no reason and that there could be cases where the first key of each vector doesn't match the :id right? But what are these cases? Or is the id just repeated twice so that the model can be used as a lookup map elsewhere?