Many websites are available at more than one domain. If you want to point multiple domains to your Pantheon site, we recommend choosing one primary domain and redirecting the rest to it. This will improve your search engine rankings, as Google et al. penalize you for duplicate content at different addresses.
- Pantheon help page: Domains and Redirects
Do not uncomment either block until your new DNS record is in place, unless you are a developer and have edited your hosts file appropriately.