Pages with zero organic traffic over 12+ months, near-duplicate content covering the same query from multiple angles, and genuinely outdated information that can't realistically be updated are the clearest candidates — not just "old" content that's still accurate and occasionally gets traffic.
A 301 redirect to the closest relevant live page preserves whatever link equity the pruned page had, rather than sending that value into a dead end. Pure deletion without a redirect strategy wastes the one benefit pruning can actually provide.
Crawl budget and overall site quality signals genuinely improve when thin pages are removed — but the effect takes a full crawl-and-reindex cycle to show up in rankings, so judge results after 4-6 weeks, not immediately.