I could see this being useful for people with somewhat unusual spending patterns that involve a lot of spending in categories other cards don't bonus. (onemileatatime.boardingarea.com)
Since the card earns double miles for spending in all categories, each dollar you charge to the card is earning you two cents of travel. (rewardexpert.com)
It earns 2.0 points per dollar spent in any category. (rewardexpert.com)