Large libraries accumulate pages that made sense once: event announcements from 2019, duplicated tag archives, thin posts written for a keyword nobody searches. They rarely hurt directly, but they consume crawl budget, dilute topical focus and make the site look thinner in aggregate than it is.
Prune with evidence and caution. A page with no traffic may still hold external links, so check before deleting: redirect it to the closest relevant page rather than returning a 404. Merge where two pages cover one intent, improve where the topic still matters, and remove only what nothing links to and nobody visits.