Purpose of newTVarIO

[tomjaguarpaw]

The Haddock for newTVarIO says:

IO version of newTVar. This is useful for creating top-level TVars using unsafePerformIO, because using atomically inside unsafePerformIO isn't possible.

But the Haddock for atomically says:

Using atomically inside an unsafePerformIO ... subverts some of guarantees that STM provides ... If a nested transaction is attempted, an exception is thrown by the runtime. It is possible to safely use atomically inside unsafePerformIO

So maybe it is possible, but you can't then run atomically on top again?