FloatOut: Float to top-level only vs. floating iff there are no free variables

This is the config record for FloatOut:

data FloatOutSwitches = FloatOutSwitches {
  floatOutLambdas   :: Maybe Int,  -- ^ Just n <=> float lambdas to top level, if
                                   -- doing so will abstract over n or fewer
                                   -- value variables
                                   -- Nothing <=> float all lambdas to top level,
                                   --             regardless of how many free variables
                                   -- Just 0 is the vanilla case: float a lambda
                                   --    iff it has no free vars
...
  floatToTopLevelOnly :: Bool      -- ^ Allow floating to the top level only.
  }

I wonder what the difference is between floatOutLambdas = Just 0 and floatToTopLevelOnly = True. Perhaps it is relevant when the RHS of a freely floatable binding has unlifted type? When would we ever float that? Puzzling.

We seem to use floatToTopLevelOnly for static pointer floating exclusively.