MacUser provides an in depth look at one useful new feature in Mac OS X 10.6 Snow Leopard: Wake On Demand.
Prior to Snow Leopard, you would have to make your Mac never go to sleep if you wanted it to provide file or print sharing services at any time. This new feature will wake your Mac over Ethernet or even Wi-Fi networks.[Wake On Demand] is Apples name for a new networking feature that lets a Snow Leopard Mac go to sleep while a networked base station continues to broadcast Bonjour messages about the services the sleeping computer offers. The base station essentially acts as a proxy for the slumbering Mac. Advertised Bonjour services includes file sharing, screen sharing, iTunes library sharing, and printer sharing among others.
There is a specific combination of hardware that is required to accomplish these tasks, however. Apple says you need an AirPort Extreme Base Station (2007 or more recent) or Time Capsule (2008 or more recent) with the latest firmware. MacUser found that in order to wake your Mac by Wi-Fi alone, you would need a 2009 Mac. To see if your Mac supports this 'Wake on Wireless' option, you can look at your System Profiler.
Apple details how this could be used to offer full time support for iTunes Sharing, Printer Sharing, Back to My Mac, and more. Mac OS X 10.6 Snow Leopard was officially launched today.
Article Link: A Closer Look at Snow Leopard's Wake on Demand Feature