Comment 10 for bug 391839

Actually, as I see it, it should be possible to put .hidden files in any directory not just the /, but even so, the overhead will not be much to worry about. Most directories ordinary users will visit contains stuff they want to see, so these directories will most likely not have a .hidden in them.

The most common use of this feature will probably be to hide things like /etc, /dev, /proc, /boot, /usr, /lib,... and other top level files that the sysadmin feels is disturbing to his users. Some of them could perhaps be hidden by default, but that is something that could be tested out on real users once the feature of supported .hidden files is included.