Windows server can be used for hosting websites(IIS and also apache can be used), yet there are many uses: You can use it as a
DHCP server(for assigning IP addresses dynamically in your network),
File server (for sharing files on the network),
Active Directory(Provides a variety of important network services especially used in organizations), use it to run
ISA(Firewall) for securing your network, you can also use it if you wish to use
Microsoft Dynamics CRM in your business, setting
Windows Sharepoint Services
There are even more uses for a windows server, but thats what I can think of right now :)
Nothing. You just have to know what you need to do and see if it matches your request.
But I dont think you need Windows Server at home. XP or 7 will do most of what you think about.
True, setting up Windows Server at home use can't be much useful except if you want to use it for testing or learn how to use it for working with it later.