I was using my Opinel to tear down some cardboard boxes one night, and couldn't be bothered using the locking ring. I pulled the blade out, pushed it back in, and the blade grabbed onto the cardboard. The knife folded up rather abruptly. I didn't cut myself, because my reflexes were faster than I had suspected, but I could have easily cut through a tendon. I found it quite unnerving, and have never neglected to use the locking ring ever since. In the end, it is an issue of safety. And ease of use, as mentioned above. Play it safe, use a folder with a lock. And one handed openers are great. Why aren't we still driving model T fords? We have better designs now. Its the same with knives.