The GDI Construction Yard
It is the goal of attacking, take out the Construction Yard means game over for either you or your enemies. It also controls many aspects of the game. Its level is responsible for setting the amount of resource fields you can have. It also dictates how fast your base will repair. You stop getting more resource fields at level 25 when you cap at 40 fields. A large portion of players stop upgrading since it's apparent purpose is no longer needed but pay the price when getting destroyed with a level 35 base and a level 25 Construction Yard.
The Construction Yard is also the toughest of the structures to take down, of course right? If it would be too easy then it wouldn't be too challenging. The best place to put your Construction Yard is either at the top left or right, or right smack in the middle. I find the far right better as it can buy some time in a war situation, the player needs to move their units, even with a scroller, sometimes, that fraction of a second will decide if either you win and live to fight another battle or lose and rebuild.
Not a whole lot else about it, take it out, you win. Get yours taken out, you lose, plain and simple.