Here's an example of how with a speedlight you have more control over your environment. The photo on the left was shot with natural light. To properly expose my subject the background went almost completely white. With the use of a speedlight you have the option of bringing out the detail of the background or make it completely black. When you using flash the two main components of exposure are shutter speed and aperture. The shutter speed controls the available/ambient light and your aperture controls the exposure from your flash. We will drill this into your head during my workshop until it becomes second nature.