Taking triangles off a corner is called a chamfer. If you're cutting it off, the material ends up on the floor or vaccines up, then recycled into new stock
The corners of their papers were all docked[1]. Recycling paper is certainly possible, just not terribly efficient. Throughout the story, they're extremely resource constrained. My question isn't generic, it's "how the hell does this aesthetic choice survive in that environment".
[1] https://www.famefocus.com/tv/33-things-didnt-know-battlestar...