Open Chrome dev tools on any site you know has a source map included, click sources tab and you will immediately see why including source maps on prod is a bad idea. You will get a tonne of information on project structure as stored on disk. This is a particular problem for modern sites that use a component based framework. I.e every view has its own controller, view and css partial.
On a site like this you will see the entire project file and folder structure as stored on the disk. This is dangerous for various reasons, not least the broad partial path disclosure and naming conventions you are giving away.
https://security.stackexchange.com/questions/113480/should-javascript-and-css-map-source-maps-be-included-on-production-servers