I have been reading about enabling source maps in production. Webpack recommends it itself. But what is the cost associated ; in terms of performance and not the build time ? Does the browser end up downloading all the maps over HTTP ( I could not find the calls under the network tab , but the code was available for debugging ). All the HTTP calls that download the map should be a concern if I have understood it correctly .
Provided that you're using a source map setting that produces a separate source map file (check here which source map settings are suitable for use in production environments), the browser will only load them if source map downloads are enabled (at least on Chrome it's a configurable option, I don't know about other browsers) and the developer tools are open.
So, for regular visitors of your website, there won't be a noticeable performance impact.