"This white paper compares deploying secure web gateways as software or appliances on-premises vs. as a cloud-based service. Lower cost, fast implementation, rapid scalability and less administration are all good reasons to adopt SaaS and cloud-based applications.
In addition to these benefits, cloud-based secure web gateways can also provide better security and faster performance than appliances or local servers. It discusses a number of advantages of cloud-based solutions that appliances cannot match, such as:
Better defense against zero-day threats and spam servers;
More comprehensive signatures and URL databases;
Supporting increased security for remote users."