Switching...
I too recently purchased a 3805, and now I'm (somewhat) regretting not waiting until the 3806 came out. Basically the HDMI switching allows you to take multiple HDMI devices and run them into your receiver, and have one HDMI cable out to your display device (TV, projector, etc.).
If your TV has only one HDMI input (like mine), and you have two HDMI inputs (HD cable box and DVD player), you get to play the switcharoo game with the cables everytime you want to use your DVD player or watch cable TV.
You can buy an external HDMI switching box or set up a "poor man's" switcher like I did and buy a little HDMI extender. This allows me to change the cables in front of the TV without digging around the back.
Bottom line (for me anyway) is HDMI switching allows for a seamless integration of multiple devices, and prevents the need for actually getting off your butt to change video/audio inputs.