All sorts of things can happen when one person writes and deploys. I know someone who worked in the IT department for a large cell phone company. At the time, working there meant free phone service. One of the devs was a heavy user of the free phone service and so was his large extended family. His job was to maintain the billing code. After several questionable incidents at work, HR got involved and he was perp walked out of the building. Due to the circumstances surrounding his departure, his cell phone accounts were checked to ensure from this point on, he would get a bill. Although his account showed a number of active phones, his balance was always zero. The code in source control was checked and there was nothing in it which provided a reason why his bill was zero. Upon further investigation, my friend noticed the version number in production did not match the version number in source control. The code in source control was compiled and a huge balance appeared for the former employee. If someone else had deployed the code in source control, this chicanery would not have been possible.
This is an interesting read, so go check it out.