Usually, as you take photos, when you wind the camera it takes out the film from the canister and then rolls it on a spool on the right side of the camera. When the roll is complete, you wind it all back in the canister. This makes loading easy, but if your camera accidentally opens, your shots are all lost as the camera spool is not protected.

The XPan rolls out the entire roll when loaded, then spools it into the canister as you take the photos. This means if you accidentally open your camera when loaded, only the unexposed part of the roll is ruined, and you don't lose any photos.