If you're familiar with camera gear, most of us know that the aperture of the lens is one of the factors that controls the amount of light entering the camera. It operates like the pupil of your eye. When you walk into a dark room, your pupil opens up to allow more light in. In contrast, when going from a dark area to a bright area, the pupil becomes smaller to reduce the amount of light. The same thing is happening with the aperture of the lens. The photographer opens up the aperture in dark situations to allow more light to enter the camera and strike the film or digital sensor.
But there's another aspect of aperture that we should take into consideration with every image. It helps control how much of our image is in focus, and this is a major decision in the artistic process. Changing the depth of field can greatly alter the way an image feels and, at times, can make or break your photo. Take these two images for instance. Same composition, same lens, but I changed the aperture to create two images that are quite different from one another.
With this first image, I chose an aperture of f/4 for "shallow" depth of field or not much in sharp focus.
For this next image, I chose an aperture of f/40 for a lot of depth of field/lots in focus. Notice how the background is no longer out of focus and has even become distracting. Is either wrong or right? No...it just depends on the look you are going for.
Ultimately, I went for the softer look simply because I liked it better. I processed the image with Lightroom and Color Efex Pro4 with the "pastel" filter. Experiment with your depth of field. Keep the images and make your creative decisions back on the computer. And have fun!