If your web server is behind a NAT firewall then you will probably find the IP address easier to use. Say
www.example.com resolves to 98.76.54.32 (public external IP), but the web server has an internal private address 10.98.76.54, you cannot use the name
www.example.com for your named host because it will resolve to the wrong IP address.
On the other hand, if you web server has public IP addresses directly bound to it, you can use the name then the virtual host will be bound to the IP address that matches the name and if you move the config to e new web server nothing in the config will change, just make the dns entry change and off you go.
So there is an argument in favour of each method, I guess it depends on your situation and what works for you.
By the way, you cannot use name-based (host headers) virtual servers for HTTPS with ssl certificates on apache, I believe there is a way to do this on IIS with Multiple SAN names on the certificate.
