Did you ever watch a DVD and afterwords check out the special features? Among them were probably several deleted scenes. Scenes that contributed to the movie, but were cut from the final for one reason or another. Perhaps they didn't fit the time constraints of the movie, or they just fit in too awkwardly. Either way movies go through a lengthy design and development process including numerous cuts, and revisions, and games are no different. Games through Alpha, and Beta design stages, and just like in movies there is often alot of content that doesn't make the final cut.
While this should come as no surprise considering the long development schedules games these days go through did you know there is a ton of people out there who study this stuff extensively? You'd be surprised to see what was cut from your favorite game. Even games as old as the 80s carry Beta and Cut content. Did you know for instance, that Centipede has an unused enemy, the grasshopper. You can find the sprite for the grasshopper enemy in the final game by viewing the game's internal test menu. Check the below link. In the bottom right hand corner on the other side of the Scorpion you can see the unused grasshopper enemy's sprite.
Sites like The Cutting Room Floor http://tcrf.net/The_Cutting_Room_Floor and The Lost Levels discuss not only unreleased content found in games, but games that never got released as well. Thanks to generous collectors, and those dedicated to preserving the work of game devs everywhere even completely unreleased games can still be made available and preserved. I don't want to go on too much about this stuff, because if its interesting you'll read more on your own. Here's some links below to some really popular games that have tons of unused content that are great to read about.
The Legend of Zelda Ocarina of Time - http://tcrf.net/Ocarina_of_Time
Goldeneye 64 - http://tcrf.net/Goldeneye_007
Banjo- Kazooie -http://tcrf.net/Banjo-Kazooie
Super Mario World http://tcrf.net/Super_Mario_World
Grand Theft Auto 3 - http://tcrf.net/Grand_Theft_Auto_III
Search your favorite game at : http://tcrf.net/
One of my old Castlevania Beta articles from Unseen 64 http://www.unseen64.net/articles/castlevania-64-beta-analysis/