Long sentences can serve as a way to break up the rhythm of prose: after a series of short sentences, a long sentence can force the reader to mentally "pause" to parse the contents of the sentence, or even just to figure out what the resulting sentence structure conveys, especially when a later part of the sentence calls back to an earlier part, turning the prose from a straightforward linear expression to a rhythmic loop, or even a self-referential construction.

Short sentences are fun too.