Road bikes with drop bars and really skinny tires are not upright. The advantage is aerodynamics, which in cycling is a huge effect.
The upright riding position is more present in MTBs, hybrids, and cruisers. They allow you to see around you a little better and many people find this more comfortable. However, you will be hit with the wind and it will slow you down considerably. At slow speeds, such as 10 mph or less, it is barely a factor. But if you ride faster than the old lady down the street...like at 15 mph and up, you will definitely notice the wind resistance.