Transmute will take as much alUSD from your stake as you can convert into DAI, burn it and send you the DAI. If that equates to a 100% alUSD😃AI conversion of whatever your stake was, then you effectively also exit.
Transmute & Exit will take as much alUSD from your stake as you can convert into DAI, burn it, send you the DAI and all alUSD that was left untransmuted. You'll effectively exit your position no matter if you were able to fully transmute your alUSD stake or not.