Everyone is always talking about placing your subject off-centre when composing images. However, placing your subject in the centre can work wonders for your image too.
This kind of placement can be a great way to highlight size. Depending on how much space there is around your subject, you can either create the illusion of smallness or make an object look grand. Choosing this framing method also lets you direct the attention of the viewer immediately to your subject. For example, when shooting landscape images, placing a single subject such as a tree, a human figure or even an interesting structure in the centre can make the entire frame look striking.
This framing method works well when you are postprocessing your images to have a soft focus effect or even when you are adding a vignette. Ultimately, rules are meant to be broken. But it is important to know what you are doing.