It’s generally a good practice to minify and combine your assets (JS & CSS) when deploying to production. This process reduces the size of your assets and dramatically improves your website’s load time.
Source maps create a map from these compressed asset files back to the source files.
This map allows you to debug and view the source code of your compressed assets, as if you were actually working with the originals.
Take a look at jQuery minified & combined code that was generated from the original. The code practically unreadable and would be difficult to debug.
But, as we all know, no matter how thoroughly you test, sometimes bugs fall will through the cracks. This is why it’s useful to debug Javascript code in production, and that’s when source maps come in handy.