What is the reason for additional blind

[moris]

Can someone please explain the reasoning for having an additional blind when someone gets knockout in those blind/button position. I always hear people say there has to be at two blinds when someone gets knocked out in those positions. HUH?? BUT WHY??? I just don't understand. Why not just a regular 1 big and 1 small? The house still gets their cut right? Someone please explain the logic for posting an additional blind.