A nit occurred to me: A lot of officers do a lot of their businesses arresting drunk drivers, even with relaxed laws with drugs, things like driving under the influence and second parties found liable for being negligent in letting people drive or use machinery while stoned means that a lot of “business” for the police will still be there; there is also like in Colorado the issue of lower quality illegal pot still sold because it is cheaper than the legal one. (I can see the unemployed officers finding work as tax enforcers).
Also, tobacco smuggling tells me that in many places there will be still work to do to by controlling that and also the legal traffic.
Still, the important thing to me is that we should drop the idea that just the simple act of smoking marijuana or to sell it and trade it deserves prison, RAND and Cato Institutes report that it is more likely that a positive fiscal impact is to be expected with the change if we legalize it nation wide.