Q. With System Center Configuration Manager (SCCM) 2007, why would I use secondary sites?
A. SCCM 2007 has a new Branch Distribution Point (BDP) role that’s designed to run on any type of hardware, which could be a server but it could also be someone's workstation out at a remote branch providing its running Windows XP or Vista. Another advantage of a BDP is that it downloads its content from a main Distribution Point via Background Intelligent Transfer Service (BITS), which lets you schedule and throttle the download of content via native BITs features. Why does this affect secondary sites? Secondary sites are not supported by SMS or SCCM clients for anything really and their use in SCCM 2007 is only for their ability to define bandwidth restrictions between sites to allow control of the traffic via channels. If you can replace a secondary site Distribution Point with a BDP and use BITS to control the traffic, a secondary site is no longer required. This means secondary sites are really only used in SCCM 2007 to control bandwidth in situations where a BDP is not an option.