Here is a basic Final Cut Pro tutorial on how to set the undo and redo allowances, what it does, and what to consider when setting it.
Non-linear video editing in really a non-destructive form of video editing. What this means is that it does not make alterations that are permanent to the base footage, but instead acts as a way to essentially media management different clips within your project file. The basic premise in this format is that you can undo any of the decisions that you make and it will not ruin your footage. You want to extend the ability to undo decisions in a way that does not permanently alter your working file, also. This will give you the freedom to try different things and be truly creative as you work. In Final Cut Pro there is a built in function that allows you to undo your work, and then redo it if you like. To make this undo function in Final Cut Pro work in your favor you have to customize it to fit your needs.
Redo the Cut
You have to set the amount of undos that you will allow in your Final Cut Pro project. This means the number of actions you can go backwards from using the undo function. For each action that affects your project you can move backward, as long as you have set your Final Cut Pro undo function to a number of times that is equal to or greater than that number. You can then always redo the actions all the way back to when you first issued in undo command. Final Cut Pro is usually set as a default of ten undos allowed, but you can go all the way up to ninety nine. You may not want to do this on older or less powerful computers as this is going to slow you down somewhat. It also allows you to go so far back that you may end up making a mistake that is not possible to fix, especially since redo only exists as long as you do not go back with undos and then make a change. If you want to adjust your Final Cut Pro undo function you will go to the upper task bar and select Final Cut Pro. From here you are going to select User Preferences. In the User Preferences window you will find Levels of Undo as the first option in the left hand side. Here you can just enter the numerical text of the number of Final Cut Pro undos you want to allow.
Performing the Undo/Redo
If you actually want to perform an undo action in Final Cut Pro you can do this manually by going up to Edit and selecting the first action, which is Undo. Below that is Redo, and you can select this to undo your undo, as it were. It is even easier to use the keyboard shortcuts, which is Command and Z for Undo and Shift, Command and Z for Redo.