Recommended for large data files, Vector Data Regionation automatically optimizes your files by limiting the number of points displayed at higher altitudes. This is similar to the technology used for Gigapan Photos (in the Gallery layer) in Google Earth; as you zoom in, you'll see increasingly more points.
You can access this feature by clicking Tools > Regionate. Select a KML file to regionate, identify a folder on your computer where the regionated files will be stored, and click OK to regionate your data.
Watch this video to see how Vector Regionation works:
Note: If you're trying to regionate a file that is not in KML format, you'll first need to import your file to convert it to KML.