IIS supports multiple Web sites on a single server. To create and host multiple Web sites, you must configure a unique identity for each site on the server. To assign a unique identity, distinguish each Web site with at least one of three unique identifiers: an IP address, or a TCP port number or a host header name. To host more than one Web site on a Web server, you can assign a unique IP address to each Web site, designate a non-standard TCP port number for a Web site, or use host headers. But how do I choose what is best for me? Read on!
Of the three methods, it is more common to use host headers than to assign unique IP addresses to Web sites or to use non-standard TCP port numbers. Performance wise, there is hardly any difference between these options.
It all boils down to flexibility that you going to need.
Host Headers advantage: Organizations that host multiple Web sites on a single server often use host headers because this method enables them to create multiple Web site identities without using a unique IP address for each site. Host Headers are cost effective as reserving public IP addresses cost money. Manageability is another great advantage if you host too many sites under the same IIS server. DNS configuration and server configuration is much easy to manage.
IP advantage: It is lot easier to implement SSL if each site has its own IP address. You just need a single certificate for the name. SSL with Host Headers requires a wildcard server certificate that is implemented and synchronized across all sites that share the IP.