The Supply Depot is a building constructed by Terran for the purpose of providing supply. Analogous to the Protoss Pylon or Zerg Overlord, it enables the construction of new units. Unlike Overlords and Pylons, however, the Supply Depot does not have any additional abilities. Supply Depots also do not build any units. Each Supply Depot raises the Terran's population limit by eight.
Supply Depots are also used for strategical purposes such as Wall-Ins, or another use for them which is to be placed near other Terran buildings to create obstructions that enemy units must walk around, giving Terran time to out-micro his opponent, as in the Sim City. Because SCVs can repair Supply Depots, their active repair during an opponent attack can further provide valuable time for the Terran player to produce or shift defensive units.
Beyond these tactics, Supply Depots take up significant building space, particularly by the late game where they can consume a significant area of the Terran main base. This prevents other buildings from being built in the space and can disrupt unit movement. As such, the Terran player must decide early on where in the base to dedicate space for Supply Depots, particularly as the Supply Depot cannot be Lift Off.
During dropping attacks, opponents will often target Supply Depots, as their destruction will disrupt the Terran supply, thus halting Terran unit construction until new Supply Depots are rebuilt.