Short answer: the academic paper that founded the GEO field proved, through controlled experiments, that including cited sources, verifiable statistics, and direct quotes from experts increases the odds a generative engine uses your content as a source — by up to 40% on some queries.
The same study found that keyword stuffing has a negative effect on citability — unlike traditional SEO, where some degree of repetition is sometimes tolerated.
Every relevant claim in your content should be traceable to a specific, dated source, rather than standing as an unsupported opinion — the same standard this site tries to follow in every article.