Have you ever been travelling on a train and you see something out of the window that you just must capture. And then by the time you've got your camera out and in position, the view has changed. It's not just the difficulty of taking photos while travelling at high speed. The train might dip into a channel cut in the bank, or the view is blocked by another train speeding by or some other obstacle blocks my view.
With a digital camera, I can click away until eventually I get the shot I wanted. Success!