Having a larger ribcage will improve your breathing capacity, posture and organ function.
From an aesthetic point of view it will give you a wider back and broader shoulders, therefore, giving you a better v–taper look. Of course, we are all different shapes and sizes, and the more mesomorphic someone is, the more likely that they will have a larger natural v-taper than most.
But people like Arnold Schwarzenegger, Stuart McRobert and Paul Kenso have all reported increased ribcage size by doing certain exercise. Even in Eugen Sandow’s book Life Is Movement you see pictures of people who have improved their ribcage size and posture with exercise.
If you want to see some scientific proof on how ribcage size, along with Idiopathic (unknown cause) Scoliosis, can be improved with exercise, take a look at this report.
Improved Chest Expansion in Idiopathic Scoliosis after Intensive, Multiple-Modality, Nonsurgical Treatment in an Adult
Martha C. Hawes, PhD; William J. Brooks, DO