Help and Support
"• You start the Disk Cleanup utility, click the More Options tab, and then click Clean up under System Restore. When you do this, all restore points (except the most recent one) are deleted.
• You are running low on disk space, but not so low that System Restore stops performing. System Restore deletes some of the restore points, but not all of them. This occurs because System Restore uses a First In First Out (FIFO) process to decrease the size of the data store to approximately 75 percent of its maximum size when the data store reaches approximately 90 percent of its maximum size. The maximum size may be the default size, or it may be set by the user. System Restore performs this deletion regardless of how much disk space you have."