Lines, in composing pictures, are important.
Horizontal lines are the main type of line we see – the horizon being the main horizontal line we encounter.
And here’s what they do (in a slide from my composition workshop):
Can you see how this looks silent, stable? I can imagine sighing, almost, when I see this. Layers of horizontals do that. Keep that in mind when composing pictures. Use horizontals when you want to emphasize vastness and quiescence, e.g. by taking pictures in landscape mode.
A tip: avoid having a main line in the very centre since this divides the image unnaturally; and keep the horizontals overall horizontal: a slight tilt is annoying.