There's a point beyond which you spend more time proving things about your code than writing it, all the way up to the point where your ability to prove things

There's a point beyond which you spend more time proving things about your code than writing it, all the way up to the point where your ability to prove things about your code in your chosen type system starts to affect the kinds of solutions you can construct, and a different kind of complexity creeps in; representational complexity rather than implementation complexity. This can be a source of error, not just inefficiency.