As a general rule, I am all for defining specific aliases of fundamental types, type-safely if possible. I don't think this changes my argument materially, though. Real world applications of programming always come down to processing data of known, concrete types at some point. And at that point, all the power you get from saying things like there's only one possible implementation of a function f :: a -> a immediately go out of the window, because you don't have a value of type a, you have a value of type SomeConcreteTypeThatIKnowThingsAbout.

In my experience, though of course yours may differ, there are very often still many plausibly correct implementations of functions working with those types and many ways to combine them that might make sense and that would satisfy the type checker. The idea that specifying the types alone is a viable substitute for proper documentation of the real meaning of the functions just falls apart at that point.