49. While that may be accepted, supervision on probation is not ordinarily seen as part of the deterrent component of sentencing. In general terms, it is regarded as rehabilitation, as opposed to, say, community service work. See Mackenzie G and Stubbs N Principles of Sentencing (Federation Press: Sydney, 2010) p 163. While it is not only undesirable, but also realistically impossible to categorise sentencing options by a supposed single purpose they might serve, it is important to bear in mind the value and intended effect of sentencing options. Thus, unless actual supervision is required for a rehabilitative purpose, then it is not appropriate to make a probation condition: R v Marquis [1974] 2 All ER 1216 (at 1218). Indeed, as was observed in Harding C and Koffman L Sentencing and the Penal System (Sweet & Maxwell: London, 1988) at p 231, the consent of an offender was originally required before a probation order was imposed "to emphasise that such an order is non-punitive in nature; indeed, a probation order is imposed 'instead of sentencing' the offender". This cannot entirely be accepted now, but this genesis is a salutary reminder that it is not appropriate to make a probation order longer in order to impose some purported punishment presumably by making the offender interfere with his or her life by having to attend on and being subject to the direction of a probation officer for longer than is necessary to provide the supervision required for rehabilitative purposes.