From Microsoft/types-publisher #81:
Using –save-dev is fine when you’re writing a simple application, and
it won’t be used as a library. The problem comes along when you might
have dependencies. If you stored your type declarations in your
devDependencies, your consumers would not automatically get your type
declarations. They’d then have to manually add your declaration file
dependencies as their devDependencies.Given that breaking consumers is a worse problem than slightly-larger
packages, we’ve made –save the default in our documentation.