Andy Brownsword lays out an argument:
Code is an ever moving target. Version control and documentation only go so far, if they even exist. Sometimes all you have is the code in front of you.
This is why I always start stored procedures with a header.
There was a time I strongly resisted this idea, but if you are diligent about keeping this up to date, it can be very useful for record-keeping, especially if your company has a tendency to switch source control systems and not keep the history between moves.