sometime when I was on the outside of home and browsing forum I have to maintain the security to hide my identity then I need to hide my forum name for not to be noticed by someone . And that is what these scripts do.
If the only need for such "turning off" is just to hide one's username on top but it doesn't cut across previous posts made, I don't see its usefulness. If anyone doesn't feel comfortable people peeping into their devices while they open them in open space, then it's only reasonable not to open it at all when in such place(s). Sometimes, we throw ourselves into unnecessary secrecy by hiding things that aren't even relevant hiding. That's the way I see this approach.
I think it is inevitable or not easy to be avoided. There may be a time you necessarily need to use the forum but you are in the public place. It will make sense if you can continue to use the forum while hiding your data than not to use at all. The former means you have freedom to do whatever you want because you can maneuver your ways while the later means you are constrained.
I remember LoyceV saying that he uses Loyce mobile while on transit or so, that also shows that you can have the need to use the forum in the public place.