Shadow subsystem can leave no trace of operation; 2. Prevent virus intrusion, attack, Trojan horse attack and so on; 3. When you need to Download E-mail with suspicious attachments; 4. Test and debug new software without any worries and delete garbage; 5. When you modify the registry, you can try on shadow subsystem to see if it will appear. Serious problems; 6. Use shadow subsystem on server to make it more secure and stable, and reduce the burden of administrator maintenance; 7. Trial extremely dangerous operations.