The problem is that you never know (unless you're at an airport where you can stand by and observe the x-ray scan like at PHX) if the baggage TSOs will re-pack intelligently if the box is opened.

There's another thread right now in this forum about a traveller whose checked bag was searched by TSA. They opened a large bottle of aspirin and a multi-day compartmented pill/vitamin container. They left them open after investigating and when she arrived, she found the pills, aspirin and vitamins scattered throughout her luggage.