When we talk about composing images, photographers are taught to keep the "Rule of Thirds" in mind, meaning we need to place our subject in our frame at a point one third from the top or bottom and one third from the left or right. The principle here is that the other two-thirds of the frame give the viewer's eye room to move aropund in the frame. So why are we talking about center, then?
Centering your subject is also a powerful compositional tool. It leaves no question as to what the subject of your photo is. It can help to minimize a distracting background. In the case of portraits, placing someone in the middle of the frame can also amplify their expression and mood. And, obviously, when symmetry is the intent of your photo, your subject will be centered.
In this photo, I chose to center my subject to convey the fact that he was heading straight for me as he emerged from the forest.
Make an intentional choice to center your subject in today's photo. If you have a little extra time, try photographing the same subject using the rule of thirds. Which photo do you like best? Why?