What is the spiritual significance of a patron saint?

What is the spiritual or heavenly significance of saint having a patronage or being patron saint with regards to something like a place, person or profession? Is it just a recognition of the fact that e.g. people of a particular profession have generally turned to this particular saint for intercession? Or is it a declaration that somehow makes a spiritual connection between this saint and some place? Or is it both or something else or does it just depend? Basically, if the church declares that some saint will now be patron saint for some new profession, does that declaration actually effect any change? Or is it a request made to that saint, which may be assumed to be accepted? How does it work?