Here are the scenarios as I see it.
Ptyrell GF, Ricer arso, NSG town, osens GA/surv
Vote Ricer: mafia and GA win
Vote Ptyrell: arso and survivor win
Vote NSG: arso win
Vote osens: mafia or arso win (town decides tomorrow)
Vote nobody: mafia or arso win (town decides tomorrow)
So basically town can choose if mafia or arso wins. Deciding today makes it so osens can also win as either GA or survivor. Deciding tomorrow makes it so that osens can't win. So thats why you may as well decide today