Okay, I'll admitt it, I don't think there is a direct purpose to the little square thing infront of the PFD. I have pondered it myself. The only things I could sea it a use for would be exactly stated above, either a knife or a safety strobe light. I would though lean more towards the strobe, because newer PFD's are coming out with the little square on the back shoulder as well. So if it's purpose is for a strobe light, it wouldn't be flashing in your face. Personally I wouldn't want a mile plus visible strobe flashing inches from my face. If I was to define it to have some purpose I would see it as a universal, easy accessible mount for any small device mainly a strobe, knife, or gps unit.