Leading lines are very commonly present in photography. They are mainly used to guide the eyes of the viewer towards a specific point in which the photographer wants the attention to be focused. There are other uses to guide the viewer’s eyes to the subject of the photography - with light, foreground / background interaction, contrast… - but the leading lines are probably the one easier to spot when assessing a scene, scenery or object to photograph.
Leading lines are very relevant elements for photographic composition, but they can be used for more than just guiding the viewer’s eye. They can be used to compose symmetrically, create disruption or transfer a perception of depth or harmony for example.
Roads, bridges, rivers, shorelines, rail tracks, street lights compose clear lines that may be giving many opportunities to compose well controlled photographies, and normally very pleasant to look at. On the other hand, those photographies may not be the most original or creative ones, although that should not prevent it to be a good photography.
Familiarity with leading lines is usually a great asset when intending to take photographies of scenes or subjects placed within a major and more complexed frame (in some cases being those in the background), driving attention to those, but being these lines a mere functional element to guide the viewer’s point of view.