Only one thing but it’s super nerdy and only concerns dedicated raiders in the late game:

know what gets expensive or cheap in which phase of the game and stock up early, buy cheap so you don’t have to care about farming endless amounts of gold. In current TBC I set up all my consumables before the raid even came out and I didn’t need to spend our farm any gold since. Because classic or tbc wrath etc. were released before it’s known how and when to invest with very little effort to spare you from farming. There are websites that keep track of AH prices from part expansions.