This is to amp up the SCV's support abilities while your defending your base, by allowing you to override Any of the valid turrets and use them to your advantage.
This means that overriding any turret will increase some stats on the turret, and may give it a additional ability.
Think of your SCV as a Engineering Wiz so it's capable of programming extra functionality into turrets...
Your SCV would be linked to the turret at a certain range, you can still move it, but generally being too far will break the link.
To balance it out, using the ability will use up a segment of your energy and stops energy regeneration over that amount (like cutting your energy in half and can't gain any more than that much).
Turret List and abilities:
Auto Turret - Increased attack speed (+0.5) / +2 damage to Light units while linked
Missile Turret - Increased attack damage (+4) / View + Detection Increase while linked
Perdition Turret - Increase attack range (+1) / Better splash damage against biological while linked
Telsa Coil - Overcharged Bolt Ability allows it to chain up to 3 different targets on hit, once every 2 attacks.
Siege Tank - Increased AoE radius / +2 range while linked
Mind Control Emulator - Increased duration on mind controlled zergs (buff) by two times the duration.
etc.
This means that overriding any turret will increase some stats on the turret, and may give it a additional ability.
Think of your SCV as a Engineering Wiz so it's capable of programming extra functionality into turrets...
Your SCV would be linked to the turret at a certain range, you can still move it, but generally being too far will break the link.
To balance it out, using the ability will use up a segment of your energy and stops energy regeneration over that amount (like cutting your energy in half and can't gain any more than that much).
Turret List and abilities:
Auto Turret - Increased attack speed (+0.5) / +2 damage to Light units while linked
Missile Turret - Increased attack damage (+4) / View + Detection Increase while linked
Perdition Turret - Increase attack range (+1) / Better splash damage against biological while linked
Telsa Coil - Overcharged Bolt Ability allows it to chain up to 3 different targets on hit, once every 2 attacks.
Siege Tank - Increased AoE radius / +2 range while linked
Mind Control Emulator - Increased duration on mind controlled zergs (buff) by two times the duration.
etc.