What is the history of periodically transferring parish priests?

What is the history of periodically transferring parish priests? St. John Vianney was the *curé* (parish priest) of Ars until his death (18th cen.). Even today, priests in some rural parts of Mexico stay at their same parishes their entire lives. Yet, in the U.S. it is common practice to transfer priests every (approx.) 4 to 7 years or so. When did this practice begin? Why was it instituted?