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If you use host as a capture filter, and you were say redirected from the initial site to another site, you would lose the redirected traffic. If you use capture filter port 80 though, you would capture all the http traffic, assuming you are using port 80 and not https or port 443.
Filter using the MAC address to ensure you get all traffic, including traffic which doesn't have IP headers like ARP, to and from the test system.

Hope this is helpful,

John