Explicit leading lines
Implied leading lines
(2) Lines are also used for other purposes than to direct the viewer.
They often can be used to set a mood in the picture.
depict stability, calmness, or peacefulness. Vertical lines are often used
as symbols of strength, power, and integrity. Diagonal lines strongly imply
action and speed, and curved lines can imply grace and rhythm. These lines
can also serve double duty as leading lines, of course.
overworked example of this is the use of an "S" curve showing a path or
stream leading from the foreground to a building or other subject in the
distance. The reason it's so overworked is that when it's well used, it's
terrific. But often photographers are so taken with an "S" curve, any old
"S" curve, that they put it in their picture whether it is appropriate or
not, and usually it's not.
Don't disdain the "S" curve, but use it
sparingly, and be sure it has a purpose.