It's most commonly used in note styles, e.g. in the Chicago (Note) style for all citations and in the Chicago (Full note) style for subsequent citations. It's sometimes used for disambiguation (MLA) or in the absence of creators for author-date styles. I don't think it's ever used in the bibliography, for good reason (it's much harder to find items by their short title than by the full title).
Ah, I see. I've noticed that for some imports (from PubMed, for example) the short title will sometimes just say "A Systematic Review," or something to that effect. This made me wonder whether, in using a particular style, Zotero would substitute the full title with the content in that field, which would be a nuisance in most of my use cases. So I've been removing the content from that field. Although I imagine that it would be useful for books with long titles where an abbreviated in-text reference might be called for.
I'd not waste time on removing this. If you imagine using styles that use short titles (many people never will), clean it up after import (Zotero typically auto-generates the short title by splitting before the first colon), but if you're going to be using medical/life science citation styles, you can safely ignore it.
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I don't think it's ever used in the bibliography, for good reason (it's much harder to find items by their short title than by the full title).