
click to enlarge

click to enlarge
The first picture was shot at 1/500 of a second and the second at two seconds. Notice how the babbling brook seems to babble that much more with the longer exposure. In this case, a
longer shutter speed allows you to capture more of what is going on, in this case showing a lot of water passing by, lending a soft, flowing look. The shorter shutter speed was fast enough to stop the motion of the water, giving a more crisp look.

click to enlarge
In another case, a
long shutter speed can be used to eliminate things moving around. The picture below was taken at the National Gallery of Art in Washington, DC. The ten-second exposure captured the rotunda pretty well, even to the point of not picking up the various people walking directly in front of the camera. If you look closely, you can see some blurry people to the right of the leftmost column. They were dawdling a bit long and stayed in the frame long enough for them to be visible. Keep in mind that this is a very busy tourist spot and the lack of people in the picture is in spite of their attendance that day.