Removing unnecessary code saves disk space and speeds up your computer.
Most applications are made to run on Intel and PPC computers. This means there programmed to run for 2 different configurations. But nobody has both, they either have one or the other.
So why keep configurations for something you don't have?
Well now you don't need to. Programs like Xslimmer remove the unnecessary code, leaving you with only what you need.
This makes the application run faster and also saves you disk space.
Unfortunately removing unnecessary code is the one thing that you need to pay a bit of money for.
Xslimmer is not free. It costs 12.95.
I'd say it's worth it because it does more then just remove unused code. It will also get rid of language packs you don't use (another thing to save space).
You can learn more about Xslimmer here.