Why the Window tab gets closed without closing the window?

Is the point of a small window in a shower to let the water vapor go outside?

• There is a small window in my bath/shower. I always open it when I take a shower and leave it open to let the water vapor go outside and to get fresh air in (I feel like this will reduce mold). My housemate closes the window when she takes a shower and leaves it closed. So I am always opening the window and she is always closing it. Is there a reason she is closing it that I don't  understand? Yes, I will ask her one of these days..but I'm wondering if I am missing something..

• Answer:

  If there is a window in a bathroom then you are not required to install an exhaust fan.  So, I an guessing that is the case.  As for your room mate, she may not like the draft that comes from an open window or feels less private.  It is good to have fresh air int he bathroom, but if it is a small window I am guessing that the de-humidification you get from it is minimal. Not to mention the introduction of humid air from outside or loss of heat or cooling.