Mustachepete and olivant both have good answers. Michael as an Accardo analogue, and Michael as a launderer for the rougher groups in New York. Two very interesting angles.

This year it came up from some researchers that there were made men who acted as local congressmen and local judges in a ludicrous place - Wyoming. And following the real world even further, there were made men in every state, men from each family in Nevada, button men in Reno (around the time of the Godfather series there were). Even stranger things like Bonanno members in Rochester, NY.

I always imagined in my head that Corleone men from Fredo, Neri, and Rocco operate the roadside brothels and gambling joints. Michael being a businessmen might not turn down an easy nickel in his new fiefdom.