Handlebar is an essential part of every bicycle. It allows the rider to lead her bike into the selected direction. On the other hand, it determines the biker body position. It is specially important to increase the bike comfortableness when pedaling for long distances, like in cycle tourism or great journeys on bike. This way, ache in arms, shoulders and back is greatly reduce and even it disappears because our body weight rests in our butts.
An additional advantage of adopting a more upright position on a bike by acting on its handlebar is that your field of vision is improved. This fact is much appreciated in urban riding due to the fact of you should pay attention to cars, pedestrians, other bikers and traffic signs. Moreover, initiating a ride is easier with a upright back as well as natural.
It the next picture you can see how different is the field of vision depending on your back upright: