And if it turns out to be wrong for whatever reason, you can be confident your fixes will propagate anywhere the types are defined. If the situation is extremely bad, especially the sort of thing where all the users must still do something that you can't offload entirely on to the type (such as an entirely new set of methods and flow for correct usage), you can define a brand new type and the compiler will guide you as to how to force the entire system to be fixed as you push the new type in and remove the old one.

I've done all these things in fairly high-security contexts where I had a very critical username normalization step. It's a very valuable tool.