If you're changing the design or layout of your emails & pages, you might not want your customers to receive the interim designs.
To avoid making changes to your live theme, simply follow the steps below.
Go to Emails & Pages.
Click on the gear icon on your active theme, and select "Duplicate".
Click "Edit" on the duplicated theme, and work on that duplicated theme.
Once you're done, click "Publish" on your duplicated theme! Your customers won't be affected by your interim designs at all.