[Haskell-cafe] Free theorem - what do we need it for

[Maciej Piechotka]

Some time ago I get knew about free theorem that states (omitting
undefined & co.) that there is 1 haskell function forall a. a -> a.

The property seems to be workaround by Typeable but it stills not work
for all types so it cannot be used in, for example, Monad or Functor. 

I am afraid that I fail to see practical benefits (I mean that I don't
know all implication not that I think there is no benefits).
What are the benefits of free theorem except large chance that data will
obey he functor/monad laws? I.e. what advantage it gives over the
'reflection' from other languages?

Regards

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