We tend to hold our bodies more tense than we need to and releasing that excess tension can help us relax and feel more comfortable. It can also help relieve pain, especially musculoskeletal pain.
To use this technique think of something soft and imagine one part of the body taking on that quality of softness more and more with each exhalation. After a few breaths pause and note how your body feels. Then either repeat that with the same part of the body, or allow a different part of the body to come to mind and let that part get softer for a few breaths. Continue to do this with various parts of your body shifting from one to another in a somewhat playful manner.