How do you prevent against sabotage/espionage?

One benefit of hidden finances is that someone new employee can't come in, run analysis on your books, then leave (while courting big $$) and make it themselves (and maybe poach key people who they know aren't asking for their fair value in pay).

There is a popular saying that someone's checkbook embodies their priorities... if this is the case, opening your finances would basically completely reveal your strategies and tactics. Why is Apple so secretive about their supply chain?