To be honest, I find Ryan Cavanaugh's argument against this quite convincing. It's weird to have something documented if you import the .ts file, but not if you import a .d.ts generated from it. If you want to show the value of the default argument of a function, you should probably just add it to the doc comment — not the type.

The argument is that it doesn't surface the default written within the jsdoc block comment even when provided by the developer.