In small organizations, there are usually only a few IT personnel on staff, and they're responsible for every piece of equipment in the company. Upgrades, repairs, and new deployments are all performed by these few technicians, and usually each of them is aware of what the others are doing at any given time. In larger organizations, however, this isn't always the case. Responsibilities for various corporate systems are distributed across large IT groups, and it could be that technicians working on related systems might not even know each other's names, let alone what the others are doing on a daily basis.
In large organizations, changes to the production environment take place frequently. Without some coordination of these changes, disasters can occur. Just trying to figure out what happened—never mind who did it—can be a challenge. To avoid these kinds of problems, you need to implement a formal change control process.