Practically everywhere you go in this country, it's the same thing: you pay first, then you get to enjoy what you bought. The only exceptions are restaurants and prisons.
If the maximum penalty for assault and battery is two years in the cooler, why do I have to beat the guy up first? Maybe I want to get the punishment out of the way before I have my fun. Can't I simply report to the state pen, do my two years, and then mercilessly beat the hell out of the chump of my choice after I get out? I've already taken care of my debt to society—I merely paid in advance.