Comment by JoelMcCracken

There are practical limits on global type inference; eg, sometimes writing Haskell youll be not sure what’s going on with some code that won’t typecheck, and the way to deal is break it down piece be piece, add type annotations, until you see where your mental model is failing.

This only gets harder with more type inference, as the actual issue may be far away from where the type error occurs.

This is why in haskell it is considered best practice to add type annotations to all top level definitions, at the very least.