If you extend a web application in SharePoint, a new IIS website will be created. That's one of the purposes of extending: to allow a different configuration.
The necessary bindings will be configured and maintained for you by SharePoint itself, on all servers in the farm. If you make manual changes to these settings, you'll have to do this on all servers. Furthermore, because SharePoint is not aware of your manual edits, you'll have to repeat this process for every server you add to the farm later on. If you already do this because you for example have to deploy SSL certificates anyhow, that might be ok for you.
If your only purpose is to have additional URL's for your content, you can add a new zone without extending to another website. But you still have to make manual edits to IIS. Therefore extending is still the best practice. SharePoint only touches the IIS bindings when creating a new web site, it never changes them afterwards. That's why it's also important to think about your design when creating a web application for the first time.
However, if you still want to have additional URL's without extending, you can:
- Create a new public URL for a different zone label
- Modify the IIS bindings manually