Sibilance is a literary device that works to add an additional touch to the explicit meaning of the text’s words. In contrast to the direct meaning of the words, the sibilance device conveys implicit messages with regard to the sense being discussed in the text.
The purpose of sibilance is to create an indirect effect through the text. It creates repeated sounds with either ‘s’, ‘z’, ‘sh’ or a soft ‘c’, that collectively give the sense of a hissing sound. This effect is used to achieve a dramatic effect and lay emphasis on a certain kind of meaning. If the background is of a horror story then such effect would work to emphasize on the creepy presence in the atmosphere. It could, of course, be used in other ways as well to strengthen the narrative in different ways.
Some examples of sibilance could be the following:
She sells seashells by the sea shore
Or, Bob Dylan’s All I Really Want to Do that creates a constant ‘hissing’ sound to add the rhythm to the lyrics:
All I really want to do, yeah
Is baby, be friends with you
Baby, be friends with you
I don't want to straight-face you
Race or chase or track or trace you
Or disgrace you or displace you
Or define you or confine you...
It helps to emphasize as well as add a musical touch to the words, that in turn help them to become more interesting as well as memorable. So the effect actually enhances the sense that the text is already trying to create for the reader.