If you want to promote lets say "my game" and you need to do whatever changes you need to, same as songs, literature etc etc... if you actually copyright it yourself and say it is yours before somebody else do it, then legally you appear as the owner of the material because it will be stated like that.
Then if somebody wants to sue you or whatever then its time and money consumed by it.
Now, I guess my real question is:
What are the right steps and precautions to follow when
1. You make a game
2. Present it for a non-exclusive license deal
3. When you actually give the material to the client