It's true that CUPS can print to SMB printers out of the box. This is particularly useful if you want to have a central spooler for all your SMB printers and/or have clients on your network that don't do SMB themselves. I for instance use it to print to a printer that's attached to a Windows 98 machine from Mac OS 9 and BeOS, neither of which does SMB or even has a native driver for the printer.
However, if you're in a Windows-only environment, it seems to me that it would be easier to let the clients talk to each other and just skip the SME Server.