Every picture you take has composition. Your composition is how you arrange the elements of your picture within your frame, and it has one purpose: to artistically and pleasingly draw attention to your subject. Different composition techniques can make the viewer feel different emotions when viewing your picture, and symmetry is a great example of this. In my study, I’ve found that it may communicate a couple of messages that can be useful to know.
Firstly, symmetry can stimulate calmness in a design—in our case, a photograph. This is because the viewer knows what to expect. Symmetrical composition is a simple composition; everything is in an exact place. Because of this, a glance is enough to tell our viewer what composition rules we’ve used. He immediately understands what is going on, and therefore relaxes. There aren’t any surprises for him to look out for. (This opens for the possibility to create tension and surprise by having a small part of the photo asymmetrical.)
Almost contradictorily, though, I’ve also found that symmetry can create a sense of seriousness, impressiveness, and dignity. I think that this has to do with the fact that symmetry displays rigid order. Rigid order is uncommon on a large scale in nature—where things appear random—so it puts us a bit on edge. We associate order with knowledge and seriousness; realizing it’s a deliberate choice, not something that happens by itself or through foolishness. When you see symmetry, you can tell that thought and effort have gone into a design, and you respect that. Subconsciously you may even somewhat fear its perfection and the hard work that went into it. Architects know this and often design important buildings (churches, mansions, government buildings, etc.) with symmetrical design.
While all true designs have order, symmetry puts that order right front and center. It’s simplicity only helps to draw attention to that order. That, I believe, is one reason symmetrical composition can be so powerful: there is obvious order, and that impresses us.
Of course, symmetry isn’t a stand-alone composition tool. Other factors—colour, texture, etc.—will help determine the final mood of your photo, and may, in fact, override the emotions that symmetry can evoke. If you need to create that simplicity and impressiveness, though, a symmetrical composition might be just the thing to use.