The overview tab is a dynamically generated tab, which contains all the settings that were changed and now differ from their default value. It enables you to quickly find a setting you recently changed, so you can either change it further or revert it to the default value.
Each setting in the Overview tab has a "Reset" option next to it, if you press it then the value of the setting will be reverted to the default option and the setting will be removed from the Overview tab.