The most critical areas to document in LEED are the energy efficiency and ventilation prerequisites and credits. You can't earn LEED certification without them, and you can't earn a higher level of LEED without showing strong performance.
Along with those factors, if you're not completing quality LEED documentation, you're going through extra reviews, which means extra time and money, and possibly losing credits, LEED certification levels, or even your whole LEED certification.