Typicality teams don't want people checking themselves out without someone in command knowing about them leaving. The check in screen only permission wasn't really designed so people would just check themselves in it was designed for a people who help command by checking people into a mission as they arrive.
I believe that this would lead to a conflict. If you can just check out on your own, who is going to know when you left?
We actually have a double system when it comes to check in and out. Not only do you check in with the scribe on MM, but you also must check in on paper in a basic ICS form. This covers things just in case the computers crash, or we have a network crash. When you check out, you must do so with the scribe, who checks you out on the computer, and you must sign out on paper.
During a major mission two years ago, we had a member who just left his post, got in his car and went home. Nobody knew he had gone home. It wasn't until someone went to relieve him at his post when we discovered he had gone. It took a couple of phone calls to find him. At that point we were pulling resources back in to go look for him. Needless to say he was removed from the team.