NVIDIA 3D Vision Surround renders to a resolution which is three times a standard display, for example (3 x 1920) x 1080 = 5760x1080. When you render these frames across three monitors, the monitor's bezel gaps can introduce space that was not intended to be there resulting in a disjointed image that is not continuous across all displays.
Figure 1: Gaming without Bezel Correction enabled.
With bezel correction enabled, part of the game view is hidden behind the display bezel so that the bezel appears to be part of the game. Using bezel correction produces a more continuous image across the displays and provides a more realistic experience. It is similar to looking through a cockpit window where the window frames block your view.
Figure 2: Gaming with Bezel Correction enabled.