That means they are not always necessary. Some preachers are slaves to illustrations, feeling that the congregation will be very bored with this particular passage unless there is an illustration to help along. I fear that says more about your preaching, dear brother than it does about the congregation! Sometimes, little breathing spaces are useful in sermons: that’s not an illustration and nor should it take time and energy away from the message. But if you feel that your preaching is simple enough not to need illustrations, but you must have them anyway to keep people with you….well, perhaps you need to go back to the drawing board!