The new "Publish Changes" button in Store Editor provides a new incremental page generation capability for your online store, allowing you to decrease total page generation and publish time by generating only the pages you've made changes to since your last store publish.
The "Publish All" button replaces the former "Publish" button. This option generates and publishes all of your store pages.

Please note that a publish of all store pages will still be performed. However, by not generating all pages before publishing, the "Publish Changes" option can decrease overall publish time.
When is a full publish (all pages generated and published) required?
A full publish is required: