Everybody knows that a faster shutter speed helps make a crisper shot. But did you know that when using a flash, shutter speed is how you control the exposure in the background that is out of range of the flash?
So if you want a darker background, nail your exposure on whatever you’re lighting, then adjust your shutter speed to control that which is not being hit by the flash.
When I want a rich background and am shooting during the day, I’ll typically underexpose my background between one or two stops. Sky and clouds will expose better that way, they’ll be more colorful and detail rich.
Beware, if your relying on ambient light to light the offside of your subject’s face, for instance, the area not being hit by the flash will act the same as the background. That is, it will darken and increase your shadow:highlight ratio on the face too.
Utilizing shutter speed will give you more control in your shots and your work will pop more…