It is important to keep in mind what happens to light as you alter aperture and shutter speed. Are there advantage or disadvantages?
Almost remember that aperture goes hand in hand with flash, whereas shutter speed affects ambient light.
Without adjusting the power of your flash, the only way to cut down on the effects of flash is to decrease the size of your aperture. If all settings are the same, when the aperture is set at f/22, the flash won’t have as much effect as it would when the aperture is set to f/8.
Shutter speed affects ambient light. Ambient light is the light that is around you, light that is available. This can refer to daylight, candle light, or even light from a window.
Keep these things in mind when shooting in manual mode.
Studio photographers like to overpower the ambient light by using a faster shutter speed thereby restricting the amount of ambient light that reaches the camera sensor. This gives them complete control as ambient light has the tendency to not be consistent. People in studios usually shoot in manual mode and instead of adjusting the actual intensity of their strobes and other lighting equipment, they can alter the aperture to change the effect of the strobes.
When attempting to take a night portrait, you have to slow down the shutter speed to allow more of the ambient light to reach the sensor. Night portraits are simply flash combined with a slower shutter speed.
Although not the perfect picture, this gives you an example of a night portrait. This was taken with my S95: a flash combined with a slower shutter speed. If I didn’t turn on flash, they would probably appear darker (such as the person on the left). If I hadn’t slowed down the shutter speed, the background would have been completely dark.