In real-time strategy games – like the Starcraft, Warcraft, and Homeworld series’ – the player needs to collect resources of some kind, which are then invested in additional resource gathering capabilities as well as combat units. The ‘macro’ game consists of building up an economy that can support the military forces you wish to assemble. In many games, it is necessary to collect resources of different kinds, with different units requiring various combinations for purchase. For instance, Warcraft II required players to collect gold, wood, and oil. Starcraft and Starcraft II feature the collection of minerals and ‘vespene gas’.
Combat units also vary substantially in how much attention they require from the player. Some units can just be ordered to march in the general direction of the enemy, and then allowed to attack automatically. Other units require constant personal attention, for instance because their capabilities are centred around spells or special abilities that the unit will not use automatically. A unit like a Roach in Starcraft II falls into the first category – it doesn’t require much personal attention. By contrast, units like High Templar and Infestors can only be effective if the player’s attention is focused on them quite a bit.
I think it is sensible to think of the time spent controlling a unit as a cost closely equivalent to the resources invested in it. Indeed, the player’s time is probably the most fundamental resource in such games. Every second spend developing an economy is a second that cannot be spent on scouting the enemy, harassing their resource collection operations, or performing tactical strikes with combat units.
Something a bit similar may arise in turn-based games like chess, especially when a timer is involved. When a player is under pressure to make moves quickly and accurately, the time they need to spend working out the implications for each of their pieces is a real cost. For instance, it might put useful pressure on your opponent to have a bishop well ahead of your other forces, supported from behind. But for every move from that point on, you need to think about the implications of your moves and countermoves for that bishop, and the chances of making a mistake increase.
