Imagine that the cue ball and the object ball are lined up straight and both very close to the end rail. You need to get position for the next ball which is at the opposite end rail.
You could try hitting it hard with high left, but hitting it such force makes the pocket less forgiving, and it is likely that you miss the shot. Instead, going rail first with a smooth, effortless stroke is much more natural and easy. Also experiment using high, low and left English to get the cue ball in different areas on the table.