In general, modules are not built on the client's machine to avoid potential issues related to compatibility and time constraints. Instead, it is recommended to build the module before publishing. The version of the module on GitHub may differ from what is actually published to the npm registry as most modules do not include built sources in their GitHub repositories.
For example, material-ui likely manually builds and publishes the necessary sources, as evident in Unpkg - material-ui.
On the other hand, packages like redux utilize a prepublish hook to automatically build sources before publishing via npm publish. This approach ensures that only relevant files are included in the published package, as demonstrated in Unpkg - Redux.
To streamline the publishing process and exclude unnecessary files (such as test directories and configuration files) that would occupy valuable space on the client side, developers can specify which files to include using the files attribute in the package.json file (documentation here).
Although some packages may be more confusing to navigate during the publishing process, such as material-ui, others like redux offer a clearer and more straightforward approach.