Personally I don't care if the OP posted just to get a rise out of folks or if that was an honest and sincere question. What I consider important is to answer that question so that people who might be wondering that exact same thing will have some information.
So... what purpose does OC in town serve?
1. OC is an up front in your face notice to any bad guys that I am armed and will not be easy prey. Hopefully that will be enough to cause them to decide to not attack me but to wait for someone who does look like unarmed easy prey... perhaps a concealed carrier who looks just like all the other unarmed folks wandering around.
2. OC makes it much easier to access the holstered gun and the draw is faster than concealed carry because the gun is unencumbered by any cover garments .
3. OC is a very visible example of the right to bear arms ... again... up front and in your face where it is impossible to ignore that there really is a right to bear arms. Concealed carry does not send that message, in fact, concealed carry in States that require a permit isn't even the right to bear arms in the first place but is merely the government controlled privilege of having... the government's permission (permit) to carry concealed.
4. OC is a teaching tool ... a way to teach police depts. there really is a right to bear arms and that there are consequences for hassling those who legally open carry even if the cops don't like it. There have been quite a few police depts. in Michigan who got a lesson in the legality of open carry... and the illegality of hassling open carriers.
5. OC invites questions and conversations making it an opportunity to educate the curious about the right to bear arms.
6. OC serves to make guns more acceptable to be seen in public by showing there is nothing to fear from ordinary people doing ordinary things while wearing a gun. The more people see of something the faster it becomes normal to see that something and before long always seeing it is just part of what is ... normal.
And open carry, including the open carry of a shotgun, into a library in downtown Lansing Michigan resulted in an important court case
http://www.michiganopencarry.org/?q=cadl that stopped any municipal "authority" (like a "library authority" or a "transit authority" or a "downtown development authority") from banning guns.