Whenever users install software program, drivers, updates, hotfixes and other system changing files, Windows Vista will create Restore Point by using System Restore, part of System Protection feature, where a snapshot and stored state of important system files are backed up and copied using Shadow Copy service. It anything goes wrong such as driver not working or program causes instability to the system, users can easily rollback to the previous state.
If you pretty sure that you practice safe computing and can handle all disaster yourself, you can turn off and disable System Restore in Windows Vista to release and reclaim space used by System Restore. But be warned that System Restore actually dependent on Volume Shadow Copy service as explained during the guide to change System Restore disk size limit. When you disable System Restore on a particular drive in Vista, all disk space allocated to Volume Shadow Copy will be released, so not only System Restore is disabled, but the useful Previous Versions will also not functioning.
Windows Vista, System Restore, Shadow Copy, Tips and Tricks, Knowledgebase