'&' and 'and' mean two different things in movie credits!
The ampersand is fun to draw. It saves space when you don't have much paper and saves time when you're furiously scribbling notes. Most people believe that it is equivalent to "and." And they would be correct because "&" is a logogram for the word "and."
The symbol can be traced back to the 1st century A.D. And old Roman cursive. The letters E and T were occasionally written together to form a ligature. This formed a symbol similar to the ampersand that we know today.
As far as it's meaning is concerned, the ampersand can mean something different than "and" in certain situations, such as movie credits. In this case, the ampersand means a closer relationship than "and." The Writer's Guild of America uses an ampersand when two writers have worked on a script together. They use "and" when two writers have both worked on a script but not necessarily at the same time.