Editing the KML associated with a Google Earth file gives you greater control over Google Earth. Some things you can do include:
Editing touring time
Smoothing out tours
Variable times between Placemarks
Animating features
Learn more about KML from the Wikipedia page, or from the Google Developer page and Google Reference page.
For more information, please visit this tutorial page or this reference page. If you have questions or comments, feel free to email me at ahecht<at>google<dot>com.
KML is very similar to XML, and most of the rules and functions are familiar to XML and HTML users. For editing KML on a MAC you can use the free editor Text Wrangler. For editing on a PC, you can use the free editor SciTE. Use common sense when downloading any software from the web and avoid any download links that seem untrustworthy.