301 redirects are the whole ballgame
When a URL changes, every link and every ranking pointing at the old address needs to be told where the page lives now — that's what a 301 redirect does. Skip even a portion of them and you strand the SEO value those pages earned, sending search engines and visitors to dead ends. The unglamorous work of inventorying every URL and mapping each one to its new destination is exactly what separates a clean migration from a traffic disaster. We do it comprehensively, because it's the difference between keeping your rankings and rebuilding them from scratch.