When a user or any search bot visits Magento website, the server provides a response if the page was changed since the last visit. If the content hasn’t changed, the page will be loaded from the browser cache, this positively impacts the page speed load and server speed. But if the correct response isn’t set on the server, it won’t provide the information about changes and the content downloads from the server every time.
- last modified 304 response
- if modified since 200 response