Cranes are complex buildings placed to automatically repair nearby friendly vehicles at regular intervals. Note that Cranes cannot remove Terror Drones, as a Repair Drone is needed for such an operation. The effects of Cranes don't overlap so don't place them too close to each other.
The Repair Crane serves as the replacement of the Soviet service depot from the original Red Alert 2 (in fact, the former uses the crane model from the latter, hence its name) due to the latter slowing down the game. Despite its lower hit points, higher tier, cost and power requirement than its original version, it compensates for its area-of-effect ability to repair all vehicles in its radius, which saves time for the Soviet general. It also does so for free (as do most repair operations in Mental Omega), meaning the Soviet general doesn't have to worry about losing resources that would otherwise be used for building the Soviet war machine.
Additional utility for this structure include repairing nearby aircraft faster from the Airbase so that they are able to take flight as soon as they are fully reloaded and repaired, supporting vehicular defenders so that the damage they take is reduced until the general is able to construct Iron Guards to make this problem obsolete, and reducing casualties of War Miners and other important vehicles from ambushes near the Soviet base.