SEP 12.1 has feature called "Deftach Active scan" that will run when new defenition arrives.
Normaly it take few minutes to complete but it may take too long (up to 8 hours) because it runs under "Best Application performance" and scan may pose due to machine status.
Customer may want let Defwatch quick scan run immediately when new definition arrives because it is important to scan important area of machine with latest definition set.
So it may had better that Antivirus and spyware policy has an option to configure scan tuning (Best Appliaction, Balanced, Best Scanning) for Defwatch Active as well as scheduled admin scan.