This option allows us to enable the auto-save option for the main entity form. The auto-save option saves your record 30 seconds after the update, so it is useful if you have created an account entity record and now want to make some more changes on the account record. You can open a record and make the required changes, and if you don't manually save your account record, the system will save your record automatically after 30 seconds, because this option is enabled by default.
If the Auto-Save option is enabled, Dynamics 365 CE users won't see the Save button on the entity command bar once the record is created. If you want to see the Save and Save & Close buttons, you need to disable this option.