Repairing a unit is far cheaper than training a new unit, but it still requires some resources. The open design of the facility allowed vehicles to drive on and off, allowing it to quickly repair vehicle after vehicle without delay. It was not unheard of for a vehicle being repaired on a Service Depot to also fight to defend the base allowing it to last longer in combat because of its being constantly repaired within a relatively open structure.
The repair bay allows players to repair damaged units, the repair costs are deducted from the player's credits. If a player runs out of credits while repairs are in progress, repairs will stop. Damage to the facility significantly slows repair work.