My buddy's crew had to replace a main server rack last week. They prepped for a full day of chaos, but every cable was labeled right and the new hardware booted up first try. They were sitting around drinking coffee by lunch, just stunned it went that well.
Those smooth days are the best. We always do a full walk-through with the new crew the day before, pointing out every valve and breaker. It feels like overkill until you're an hour ahead of schedule. The real trick is having everyone run through the checklist out loud, no skipping steps.