Whenever you have a strong existing line (like fence cutting through a landscape, for example) or a definite row of objects (like the flower pots shown here) running through the frame, the way that you arrange those lines in relationship to the edges of the frame can have a powerful influence in our interpretation of that scene.
Strong horizontal lines, for example, impart a feeling of stability and strength and they provide a sense of equilibrium. You know that when you have a crooked horizon in a sunset photo, for instance, that it's very unsettling--it makes it feel like the earth is sitting sideways. And strong vertical lines (trees, telephone poles, people standing) make the scene seem taller and provide a feeling of strength or even energy. Think how different it is when a waterfall is framed so that the flow of water runs from the top to the bottom of the frame rather than from side to side. The vertical framing shows force and power while the horizontal frame is much more peaceful and harmonious.
In between the two, of course, are diagonal lines. A strong diagonal line, whether it's a road going through the frame or just a row of objects (like the row of flower pots here), create a more dynamic flow to an image. Most importantly, diagonals provide a very real sense of motion and, even in a quiet still life like this one, provide the feeling that something is happening, that the composition has rhythm and flow. Try it sometime. Photograph a row of flower pots or perhaps some colored bottles on your front step from three different angles: so that they run vertically, horizontally and diagonally across the frame and see which you like best. There's no right or wrong, just a different feeling for each choice.