One common complaint I hear about Japanese youth these days is that "they sit anywhere." This statement refers to young people sitting on the ground. One reason for this phenomenon is that young people in Japan never used to loiter because they were in school six days a week and even spent Sundays participating in school events. Kids have more free time than ever now and as a result are "hanging out" in front of convenience stores, on street corners, etc. As these nascent loitering youth loiter longer hours, it's only natural that they want to do it sitting down.
So they take to sitting on the curb, the sidewalk or on the street itself. And sometimes you'll see them just squatting, a position Asians do instinctively when they want to rest but not sit on the "dirty" ground. Although you will sometimes see variations of the squat position, usually it is done by bending the knees all the way down, splaying the legs, and leaving just enough of the tush hanging down to balance the body over the heels. To Westerners, this position is very peculiar.
Yet all Japanese, at one time or another, have squatted in public. Construction people squat when taking a break, men in suits might squat when smoking a cigarette, even my neighbor does it if she thinks no one important is watching. Being that Japan is a bring-your-own-bench culture, I suppose it is not surprising that people have invented their own type of invisible chair. If we were to adopt the invisible chair in the U.S., we'd have a lot of people permanently stuck in the squat position. Perhaps that's the real reason we have benches in public areas.