Cuffing your jeans was common practice and simply a necessity before the process of sanforizing denim was introduced in the 1920s. Back then, all jeans were unsanforized. As the unsanforized denim shrinks up to a considerable 10% in length, wearers had to buy their jeans too long to not end up with jeans that would become too short once the denim had shrunk.
Nowadays we cuff our jeans to show off the selvage or simply because we like how it looks good. It is recommended to empty your cuffs for rubble, coins, and what ever falls in there, and turn down the cuffs when you wash your jeans.