To remind us men (who - after all - can't do that) that they are women.
Regards,
LOL, like crossing your legs at the knees...granted, back in the day (up until probably around 1960) it was sophisticated for guys to do that, but...now, if I see a guy doing it, I do a double take-it generally looks feminine now. Guys can do it if they work at it (if they wanted to) but...er...ahem, anatomically speaking, it is a lot more, er...uncomfortable!