Originally Posted by DakarM
no. ISO can be increased when there isn't enough available light or if you can't or don't want to use a flash.
to stop motion, ie, car driving by in day light you need a fast shutter speed.
Or you can use a higher ISO in order to get that faster shutter speed. If you can only get a 1/400th out of iso 200, then you can raise your ISO to 400, 800, 1000 ect. to get a faster shutter speed. That is where Canon's CMOS shines over others CCD's in that higher ISO's dont nesasarily (sp?) means more grain.