Live View Shooting Mode is almost exactly what it says: you're seeing what the camera's lens is seeing, but you're seeing it on the camera's LCD. Live View enables you to view and compose the shot without looking through the finder, and it's ideal for situations in which you want to, or need to, hold the camera at an unusual angle or away from your body.
Traditional D-SLR phase-detection AF sensors are blocked whenever a camera raises its reflex mirror to expose the imaging sensor, which is what happens in Live View's Handheld Mode. Since the imaging sensor constantly streams data for the LCD display during Live View operation, the mirror must be continuously held up while Live View mode is being used. Consequently, there's a brief interruption to the Live View display as the camera drops the mirror, focuses and then quickly flips the mirror back up to shoot a picture, after which Live View resumes. This is fine for relatively static scenes, but the delay in focusing, not to mention the interruption to your view of the scene, can mak