Why SSR? (Reason #14 of 3,487,659) Reading for fun increases your concentration. There are so many things that distract us all day long, requiring divided attention for shallow thinking. Reading longer texts for sustained periods requires greater levels of concentration for deeper thinking. The more you read for fun, the more you will be able to concentrate on other things for longer periods of time.
Of course, even better: (Reason #1) Reading for fun is fun.