These generally are: punishment, rehabilitation, deterrence, denunciation and protection.
Armstrong Legal: Assault Causing Death - One Punch Laws
Sydney Morning Herald: Hugh Garth, first to be charged under 'one-punch' laws, jailed for at least eight years
Sydney Morning Herald: Ineffective one-punch mandatory sentences should be scrapped, says Law Council
Daily Telegraph: One-punch laws: Has tougher legislation curbed coward-punch epidemic?
ABC News: One-punch laws: mandatory sentences for drunken violence 'a recipe for injustice', say NSW legal experts
In Informit, type in 'theories of punishment' or 'mandatory sentencing'.