If you choose Revert in either the main preferences dialog box or the application preferences dialog box (or select it from the File menu), the settings in that dialog box will revert back to the last settings that you saved.
In the application preferences dialog box, the Revert button only affects the current list in view. For instance, if you are currently viewing the "Don't switch from these" list and press Revert, the only list that will be reverted is the "Don't switch from these" list. Other lists will not be affected.