According to Gartner's report, Firewall as a Service is a firewall delivered as a cloud-based service that allows customers to partially or fully move security inspection to a cloud infrastructure. All enterprise traffic from datacenters, branches, mobile users, and cloud infrastructure are aggregated into the cloud

There are three basic types of firewalls that are used by companies to protect their data & devices to keep destructive elements out of network, viz. Packet Filters, Stateful Inspection and Proxy Server Firewalls. 

Software firewalls allow you to easily control network access on a per-application basis. In addition to controlling incoming traffic, a software firewall can prompt you when an application on your computer wants to connect to the Internet and allow you to prevent the application from connecting to the network.

A firewall is a network security device that monitors incoming and outgoing network traffic and decides whether to allow or block specific traffic based on a defined set of security rules. Firewalls have been a first line of defense in network security for over 25 years.

Firewalls are also used for Network Address Translation (NAT). This allows a network to use private IP addresses that are not routed over the Internet. ... Firewalls are also very important for home broadband users - without a home version of one of these products, your personal data is at risk.

If a software firewall is disabled, it's not just the associated computer that's in harm's way; worms -- a type of malware -- for example, can spread across a network connection, infecting all of the PCs attached to the LAN. Disabling a hardware firewall also impacts all of the devices that connect to the network.