The -tracehods command exposed some information to us about what is and isn’t being loaded into memory that we didn’t have before. Based on my experiments so far, if a ship is listed a build file for an available race according to the filters(in single player missions, the rules might be a bit different in skirmish) it will be loaded at game start. Missiles and subs used by included ships will also be loaded. Otherwise things won’t be loaded unless they’re in the .level file. Things not in that list can still be spawned on the map later, and will be loaded durring the game.
This can be used to considerably reduce load times for testing certain things!