In addition to what I post recently, some units may demand a special combination of buildings in province to be produced.
For example, a paratrooper-like infantry (such as Militarum Tempestus or Raptors) demand a Barracks and Landing pad to be built. And Field artillery, as the piece of heavy equipment, may demand a presence of Barracks and Vehicle depot either.
Another unit, that can demand a presence of Vehicle depot and Landing pad, may be a flying unit, that can attack ground targets, especially infantry. Those can be:
Astra Militarum: Vulture gunship/Avenger dive bomber
Adeptus Astartes: Storm Talon/Storm Eagle
Chaos: Hell Talon fighter-bomber/Storm Eagle
Orks: Deff-kopta/Dakkajet
Those aircraft may be fine addition to air superiority of any side of conflict, add to aviation some anti-infantry capabilities. But demands of having either Vehicle depot and Landing pad balancing this by bigger investment in production of one province.