[jayflux]

Many developers have type checking built into their IDE, so they usually know when something is wrong. Having it run again on every build (especially in watch mode) isn’t very efficient. Instead it’s faster to have type stripping as part of your developer workflow, then a full type check when you’re ready to commit.

[pjmlp]

The same IDEs generate the JS files when they are done with checking, so like why bother with a lesser solution.