To release from your foot in a bad fall.
Rubber boots do neither well.
The tighter you make the rubber boots for increased control, the more they hurt and the less they come off in a fall. The looser you make a rubber boot the more comfort and safety you will have, but you will loose control and power. The Inter-Loc System is mounted on a Carbon Fiber binding plate that is releasable from the ski. It's a screwless binding system. After six weeks in a cast I vowed never to put my foot back in a rubber boot.