So I was playing with shutter speed today just testing things, and got to 1/200. Aperture set to 3.5 and ISO set to around 100. With flash on this resulted in an over exposed image due to the flash. So I tried to increase the shutter and realized it won't go past 1/200 with flash on (this is in full manual mode and shutter priority mode) so I understand the shutter speed and how it works. But even with an ISO of 12600 aperture of 3.5 and a shutter speed of 1/4000 it is still slightly underexposed. With a very very grainy image due to the ISO. So what is the purpose of a 1/4000 shutter, and where would you effectively use it if your unable to flash to generate the light needed?