Yeah it's just a good habit to get in to. I've seen other baggers going down the road with the hard bag lid flipped wide open. I pulled alongside and pointed it out and he stopped to fix it.
I seldom lock them. Every so often I check the function of the latches, and make sure the brackets are properly aligned, and I don't really have a problem with bags coming open. Even on some pretty stiff speed bumps.
I trying to get into the habit now. Ive only had my bag pop open once, but I lost a damn good softball glove from it. I had a lot of stuff in the bag that day