The Command Center 'CC' is a defensive/utility building that all players receive at the beginning of each round. It's main feature is enabling players that are allied to share unit-producing buildings with each other.
When you spawn, the Command Center is already built. After the Command Center loses its buff, it becomes a fragile building susceptible to almost any kind of planned attack.
Generally speaking, the Command Center is only useful as a standalone defensive building within the first 20 minutes of any round. Any more than that will require more protection or support.
The can be vulnerable to nukes because, what is not.
Artillery's range is higher than that of the Command Center's, making it a huge threat if left alone unchecked. The Command Center has no way of countering artillery attacks alone, even with its damage buff. This threat can easily be faced with an army of your own, threatening the artillery that has very little health.
The explosive tank is also a unit to be wary of. It only takes 5 explosive tanks to destroy a Command Center, and the Command Center can't deal enough damage to kill an explosive tank alone on time even with its damage buff. Although a cheap alternative to the artillery, it can be very difficult to maneuver to a Command Center, especially when it is chased with cheaper troops.