If I was a Lich sitting up in my ivory tower, I would spend all my time compiling D&D minutia. I started playing with the Moldway Red Box set. There were 69 Monster types and a total of twenty spells at first level. The rules were elegant in their simplicity. Too much reliance on luck and AC for me from almost get go, but, you knew all of the monsters and with the few stats and no skills, game stats were a minimal burden during the writing phase, and NPC character generation was quick.
Today, we have 350 monster type in Monster Manual alone, but we also have MM2 and the Fiend Folio, as well as the Oriental Adventure and the exotic and interesting skills and game mechanics are scattered 12 AD&D 1st Edition books and 32 supplements. That's were compiling the data and the unified theory of D&D comes in. I have decided to compile all skills, spells, and monsters for easier access during my adventure design. One of the perks of where I am working, is that I can buy the latest edition of the MS Office Professional edition for less than the price of a movie ticket these days. One of the side projects I am working on is building the Access database for the spells and monsters available in the AD&D. The spells are grouped in schools of magic, and it is tied to locations in the game setting, where the players must go to learn these spells. The Monsters are indexed by the terrain type, level, and creature type. So, when I am considering a desert adventure on the sea of grassland that burned out a long time ago, when considering what humanoid, predator, and an giant insect to use, I just input the information into my database, and get a list of the creatures and the location of the source text for that creature. My campaign has about 350 skills, grouped by the culture, class, and social background of the characters, who have access to learn those particular skills. None of the players ever seen the big picture, and the Big Picture, as far as the Non-Weapon Proficiencies go, only rates a mere Spreadsheet.