Advantages of hardware firewalls over software firewall:
Speed: Normally, the hardware firewalls are tailored for faster response times, and hence handle more traffic loads.
Security: A firewall with its own operating system (proprietary) is less prone for attacks. This in turn reduces the security risk. In addition, hardware firewalls have enhanced security controls.
No Interference: A box, that is separated from other network components can be managed better, and does not load or slowdown other applications. The box can be moved, shutdown, or reconfigured with minimal interference to the network.
Disadvantage of hardware firewalls:
Cost. Normally, a dedicated hardware firewall costs more than a software firewall.
Difficult to install, and upgrade.
Takes up physical space, and involves wiring.