A change of image with a click or mouseover can indicate a simple alternative in place, change perception of the screen contents, alter the background, open another window, take us to another segment of text or image, initiate sound, or begin animation. Links, or the absence of links, indicate the boundaries of the structure. They control the pace. They indicate time and rhythm. They introduce media.
Links can also form the meta-language of a piece.
Consequently, while there is almost no computational difference between links, the effect of link configuration on literary style and content is significant. Hypertext did not have links. But neither did it ever actually have computational ability . Most traditional hypertexts did not have computational ability. The Turing Machines that Montfort cites as his prototypic Category 4 works are intended to accept complex input and to, within the confines of their coding, create and execute new commands.