In Bill Donahue’s, The Secret World of Saints: Inside the Catholic Church and the Mysterious Process of Anointing the Hold Dead (2011), Byliner Inc: Kindle Edition http://www.amazon.com/gp/product/B006P2X86U, he briefly describes the procedures of the Church’s saint-making process in Chapter 6. Donahue notes that “Venerable is a pretty high rank—akin to, say, four-star general or eighth-degree black belt. Very few servants [those declared “Servants of God”] get there, and when they do, the Vatican allows them some perks: You can build a church in a venerable person’s honor. You can put his image on prayer cards and build little shrines. Catholics pray to the venerable—and often allot them small plots of holy turf. For instance, the Venerable Matt Talbot, an Irish dockworker and drunkard who went on the wagon to live his final forty-one years as an ascetic, is the patron saint of alcoholics.”
Whereas Venerable Matt Talbot’s patronage is already established in the eyes of many, Donahue states in a footnote that "saints are never chosen on the basis of their patronage potential. Rather, they’re picked for their virtues and for their miracles—and then, over time, they accrue patronages...”