Manifest function of the bridge:
 
Make it easier and quicker to get from one side to the other.
Prior to its construction in the 1930's, people had to take a ferry.

Possible latent functions:
 
1.  Create a recognizable symbol for the city of San Francisco
     that will attract tourists and encourage civic pride.
2.  Provide work for people during the original construction and
     for continuing maintenance.  It was built during a depression.
3.  Allow politicians who were responsible for its construction
     to increase support for their reelections.
4.  Reaffirm the power of the state.